Shanghai-Kowloon Through Train

The Shanghai–Kowloon Through Train is an intercity railway service between Kowloon Station (also known as Hung Hom Station) in Hong Kong and the Shanghai Railway Station, jointly operated by the MTR of Hong Kong and China's national rail service (Shanghai Railway Bureau). The numbers of this train service is Z99B (being away from Shanghai) and Z100B (being towards Shanghai). Services operate along the East Rail Line in Hong Kong, crossing the boundary between Hong Kong and mainland China at Lo Wu and then continuing along China's railway network via the Guangshen railway, Jingguang railway and the Hukun railway to Shanghai. The Through Train runs every other day. The journey time is approximately 20 hours.

The stops on the route are Guangzhou East, Zhuzhou and Jinhuaxi Railway Station. Only passengers taking Z99A/Z100A (Shanghai-Guangzhou East) can disembark at these stops.

Since 1 October 2003, passengers who are taking Z99B/100B cannot disembark the train at the stops listed above, as all travelers to Hong Kong from Shanghai clear Chinese immigration and customs at Shanghai Railway Station, and once they have done so they are considered to have left Mainland China and are no longer permitted to leave the train until their arrival at Hung Hom Station. The same rule also applies to Northbound travelers who will clear Chinese immigration once they have arrived at Shanghai Railway Station. 144-hour visa-free transit for passengers who are of selected nationalities are available since 30 January 2016.

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Wikipedia