Decoding Hong Kong Bus Route Numbers and Their Prefix Letters

A Hong Kong bus route number tells you, before you check any map, whether that bus crosses the harbour, heads to the airport, runs express, or only operates after midnight. Every letter and digit encodes operational logic: route type, geographical corridor, and sometimes the operator. The system is not a perfect code. Some numbers are legacy assignments that long outlived their original logic. But the stable patterns hold. Learn them once and you can read a bus stop at a glance.

Prefix letters sit at the front of the route number and define the route type. The most common prefix you will see is K, which marks a KMB railway feeder route. These buses connect MTR stations to nearby housing estates and their route numbers are short, usually one or two digits. An X prefix means express. These buses skip large sections of the corridor they serve, using flyovers and tunnels to cut journey times on long-distance runs between the New Territories and urban Kowloon or Hong Kong Island. X routes carry a higher fare band than their all-stops equivalents.

Airport And External Routes

An A prefix signals an airport route. These are dedicated services operated by Citybus under the Cityflyer sub-brand or by Long Win Bus, the KMB subsidiary that holds the Airport and North Lantau external franchise. A-route buses have luggage racks, coach-style seating, and a premium fare tier that can be double the cost of a standard franchised bus ride of similar distance. The E prefix designates external airport area routes that serve the logistics zone and employee areas rather than the passenger terminal, with a lower fare than A-routes and a mix of standard and coach bus types.

Night, Peak And Interchange Prefixes

N is the overnight prefix. These routes run between roughly midnight and 5am when the MTR is closed, often following modified alignments that differ from the daytime equivalents. A P prefix marks a peak-hour express service, operating only during the morning and evening rush on weekdays. B is a newer prefix used for bus-bus interchange hub routes, and M appears on routes that terminate at an MTR station but are not classified as standard K-prefix feeder services. Some M routes date from the opening of the Tseung Kwan O line and use the letter to distinguish them from the older K-series.

The hundred-series block is the backbone of cross-harbour route numbering. Any route number in the 100s crosses Victoria Harbour between Kowloon and Hong Kong Island. The original cross-harbour routes were numbered in the 100-series when the Cross-Harbour Tunnel opened in 1972, and the convention stuck. A 1XX number tells you three things immediately: the bus goes under the harbour, it carries a cross-harbour fare premium, and it is operated by either KMB or Citybus under joint franchise arrangements for cross-harbour services.

Eastern And Western Harbour Crossings

The 600-series block is reserved for Eastern Harbour Crossing routes, a smaller set of services linking eastern Kowloon districts like Lam Tin and Yau Tong to eastern Hong Kong Island. The 900-series block covers Western Harbour Crossing routes, which often run express from the New Territories to Hong Kong Island using the westernmost tunnel. These 900-series routes are long-distance expresses with the highest toll regime of the three harbour crossings, and that cost is reflected in the fare band.

Route number prefix and hundred-series block conventions are not operator-specific. Both KMB and Citybus use the same prefix logic and the same hundred-series blocks. The operator is determined by the franchise boundary the route runs through, not by the number itself. A 1XX route could be a KMB route, a Citybus route, or a joint operation with both companies running departures.

Kowloon Motor Bus route numbers follow a geographical block structure that dates back decades. Routes in the 30-series serve Tsuen Wan and Kwai Tsing. The 40-series covers routes to Tuen Mun and Yuen Long. The 70-series is the North District and Tai Po block. The 80-series serves Sha Tin and Ma On Shan. The 90-series is the Sai Kung and Tseung Kwan O block. These are not rigid boundaries. A handful of routes carry numbers from a different block because they were renumbered during a network restructuring and the old number was retained for passenger familiarity.

Within each block, lower numbers tend to be older, all-stops routes that have run for decades. Higher numbers in the same block are often later additions, express variants, or peak-hour special services. An 89D and an 89X serve the same general Sha Tin corridor but the X variant takes the Tate's Cairn Tunnel and skips the intermediate stops that the D variant serves. The letter suffix, not the number block, is what tells you about the service pattern.

Long Win Bus, despite being a KMB subsidiary, operates under its own franchise with a separate number series. Long Win route numbers start with an A or E prefix and use a different numbering logic from KMB's New Territories blocks. A Long Win A33 and a KMB 33 have no relation to each other. The franchise boundary between the two operators is strict and no KMB bus ever serves the airport passenger terminal.

Citybus uses a different numbering logic on Hong Kong Island. Routes in the single digits and low double digits are the oldest Island routes, some inherited from the former China Motor Bus franchise that Citybus replaced in 1998. The 10, 5B, and 2A are core Island corridors that have run for decades. Citybus cross-harbour routes share the 100-series, 600-series, and 900-series blocks with KMB, following the same conventions. The 300-series is a Citybus-specific block for peak-hour cross-harbour express services that only run on weekday mornings and evenings.

The Cityflyer airport routes use the A prefix with numbers in the A10 to A29 range, serving Hong Kong Island and Kowloon districts from the airport. Citybus E-prefix external routes use the E21 to E23 range. The Citybus network on Lantau is limited to the airport corridor. Citybus does not serve South Lantau, which is the exclusive franchise package of New Lantao Bus. If you see a bus on Lantau with a route number in the 1, 2, or 3 series, it is an NLB route, not a Citybus route.

Some route numbers break every rule. The 2X on Hong Kong Island is an express variant of the 2, but the X suffix rather than prefix is a Citybus convention inherited from the old China Motor Bus numbering style. Cross-harbour routes obey the 100-series block rule, but some were renumbered into the 900-series while retaining short-working variants for years, creating confusion at stops. The 270A and 270B serve different New Territories destinations but share a number block because of a historical route splitting exercise.

The N prefix for overnight routes is applied inconsistently. Some overnight routes simply add an N to the daytime number, so route 118 becomes N118 at night. Others use entirely different numbers. The N8X and N8P on Hong Kong Island are overnight routes with no daytime 8X or 8P equivalents. The NLB network on South Lantau uses route numbers in the 1, 2, 3, and 4 series with no prefix letters at all, a different numbering universe entirely from the urban franchised bus system. You cannot decode an NLB number without knowing the South Lantau franchise boundary logic.

Check the destination display. A bus with a route number you do not recognise may be a short-working, a special departure, or a diverted service using a temporary number. Short-workings are common on peak-hour express routes where a bus runs only part of the full route to clear a high-demand segment. These sometimes use the same number as the parent route with a different destination shown on the front display. A 68X short-working to Yuen Long might show the same 68X number but a different destination than the full route to Hung Shui Kiu.

If you are at a bus-bus interchange and the number does not match any route on the stop plate, look for the interchange discount sticker. Designated BBI stops display a green and white decal listing the discount-eligible route pairs. The bus you need might stop at a different bay in the same interchange complex. At large interchanges like Shing Mun Tunnels or Tai Lam Tunnel, multiple bays serve different route families and the bay assignment follows the hundred-series block logic. Cross-harbour routes stop at one bay, New Territories express routes at another, and local feeders at a third.

Use the HKeMobility app to confirm the route alignment and stop location. The app pulls live data from all franchised operators and is the official source for route alignments, stop locations, and real-time bus arrivals. An operator app covers only that operator's routes and may miss inter-operator interchange options that HKeMobility shows.