A subway train has derailed in Hong Kong, injuring at least eight passengers and snarling the morning rush-hour commute in a city whose transit system has been routinely disrupted by three months of pro-democracy protests.

The fire service said eight people were injured, with five being sent to hospital for treatment.

Such accidents are exceedingly rare in Hong Kong, and there was no indication that the crash was related to the protests that have prompted the former British colony’s worst political crisis since it was handed back to Chinese control in 1997.

The crash comes after an especially violent weekend of street clashes, in which the Hong Kong police fired tear gas and water cannons after protesters vandalised a subway station and attacked government offices with bricks and gasoline bombs.

Continuing protests rock Hong Kong: In pictures Show all 35 1 /35 Continuing protests rock Hong Kong: In pictures Continuing protests rock Hong Kong: In pictures Police officers point their guns towards pro-democracy protesters after a clash at a march in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures Pro-democracy protesters throw molotov cocktails during clashes with riot police in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures Demonstrators rally behind barricades ass they are shrouded in tear gas deployed by police in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures Police clash withpro-democracy protesters at a march in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures A police officer prepares to strike a protester as clashes erupt during a pro-democracy march in Hong Kong on August 24 AFP/Getty Continuing protests rock Hong Kong: In pictures A water cannon is fired by riot police to clear the street of demonstrators during a protest in Hong Kong on August 25 EPA Continuing protests rock Hong Kong: In pictures Pro-democracy protesters use a slingshot during clashes with riot police in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures Riot police fire tear gas to disperse pro-democracy protesters in Hong Kong on August 24 Reuters Continuing protests rock Hong Kong: In pictures A demonstrator throws a molotov cocktail as they clash with riot police during a protest in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures A demonstrator swings a tennis racket in an attempt to knock back a tear gas cannister thrown by riot police during a protest in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures A protester displays a Hong Kong Independence flag during a pro-democracy march in Hong Kong on August 24 EPA Continuing protests rock Hong Kong: In pictures Riot police tend to a detained demonstrator who has been injured during a protest in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures A demonstrator uses bamboo poles to build a barricade during a protest in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures Riot police clash with demonstrators during a protest in Hong Kong on August 24 Reuters Continuing protests rock Hong Kong: In pictures Protesters are hit by tear gas fired by the police in Hong Kong on August 24 AFP/Getty Continuing protests rock Hong Kong: In pictures Demonstrators shrouded in tear gas shield themselves behind barricades during a clash with riot police in Hong Kong on August 25 Getty Continuing protests rock Hong Kong: In pictures Riot police arrest a protester during a pro-democracy march in Hong Kong on August 24 EPA Continuing protests rock Hong Kong: In pictures Police clash with pro-democracy protesters at the Hong Kong international airport on August 13 AFP/Getty Continuing protests rock Hong Kong: In pictures Protesters fall back as they clash with police during a protest at Kowloon Bay in Hong Kong on August 24 AFP/Getty Continuing protests rock Hong Kong: In pictures Police clash with pro-democracy protesters at the Hong Kong international airport on August 13 Reuters Continuing protests rock Hong Kong: In pictures Riot police move to disperse protesters during a clash at the Hong Kong international airport on August 13 Reuters Continuing protests rock Hong Kong: In pictures Commuters riding in a bus drive past protesters in Hong Kong's Kowloon Bay on August 24 AFP/Getty Continuing protests rock Hong Kong: In pictures Protester hold umbrellas as they take part in a pro-democracy march in Hong Kong on August 24 EPA Continuing protests rock Hong Kong: In pictures Riot police detain a demonstrator as they clash during a protest in Hong Kong on August 24 Reuters Continuing protests rock Hong Kong: In pictures Pro-democracy protesters block the entrance to the airport terminals after clashes with police at the Hong Kong international airport on August 13 AFP/Getty Continuing protests rock Hong Kong: In pictures Riot police spray pepper spray as shield themselves by a police van during a clash with pro-democracy protesters at the Hong Kong international airport on August 13 Reuters Continuing protests rock Hong Kong: In pictures Riot police use pepper spray to disperse protesters during a demonstration at the Hong Kong international airport on August 13 Reuters Continuing protests rock Hong Kong: In pictures Demonstrators shrouded in tear gas shield themselves behind barricades during a clash with riot police in Hong Kong on August 25 Reuters Continuing protests rock Hong Kong: In pictures Medical professionals gather to protest police brutality at the Queen Elizabeth Hospital in Hong Kong on August 13 Getty Images Continuing protests rock Hong Kong: In pictures Police detain a pro-democracy protester at the Hong Kong international airport on August 13 AFP/Getty Continuing protests rock Hong Kong: In pictures A protester is halted by police during an occupation at the Hong Kong international airport on August 13 AP Continuing protests rock Hong Kong: In pictures Police clash with pro-democracy protesters at the Hong Kong international airport on August 13 AFP/Getty Continuing protests rock Hong Kong: In pictures Police stand guard at the entrance of the departure terminals at the Hong Kong international airport on August 13 AFP/Getty Continuing protests rock Hong Kong: In pictures Protesters continue their occupation at the Hong Kong international airport on August 14 AP Continuing protests rock Hong Kong: In pictures Travellers read placards and posters left by pro-democracy protesters at the Hong Kong international airport on August 14 AP

Adi Lau, the operations director for Hong Kong’s subway operator, the MTR Corporation, told reporters that three middle carriages of the 12-carriage train had derailed.

He said it was too early to draw conclusions about the cause of the accident.

At a separate news conference, Frank Chan, Hong Kong’s secretary for transport and housing, called the accident a “very serious incident”.

“We will not rule out any possibility, but at this stage we won’t speculate on any particular suggestions,” Mr Chan said when asked about the possible causes of the crash.

He said an investigation was underway.

The MTR Corporation’s shares fell on the Hong Kong Stock Exchange at the start of trading Tuesday, but had recovered slightly by midmorning.

MTR stations have emerged as a prime target of vandalism during recent protests, apparently because protesters are angry at the company for having allowed riot police officers to enter its stations and beat or round up protesters.

On Sunday, protesters set up barricades and broke glass railings inside one downtown station, and set a fire outside another.

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The derailment occurred as a train entered the Hung Hom Station, which sits across the city’s harbour from Hong Kong Island and is also the terminus for rail service to the Chinese mainland.

Passengers were forced to leave the train, which was split into two sections, by walking across the tracks.

In March, an MTR train derailed and hit another train during a test of a new signalling system.

That crash occurred in the middle of the night and neither train was carrying passengers.