As many as six passengers were injured yesterday when a London underground train derailed at a bustling station in the second such incident on the creaking Tube network in 48 hours. The derailment brought Camden Town station, one of the underground?s busiest stations on a sunday, to a standstill as police, fire engines and ambulances services raced to the scene. The cause of the accident was unknown.

?At the moment, there are five, possibly six injured, including one man possibly with a broken leg,? said Colin Markham, a spokesman for London Transport Police. The derailments are particularly embarrassing as the capital vies to host the 2012 Olympics. The last two carriages of the train derailed as it entered Camden station on the Northern Line, which bustles on a Sunday as Londoners and tourists flock to nearby markets and cafés.

The accident follows a derailment at Hammersmith station on Friday on the Piccadilly Line that rail authorities said may have been caused by a broken rail. In January, some 32 people suffered minor injuries after a packed underground train derailed as it pulled into Chancery Lane on the Central Line. That accident disrupted services on that line for weeks and left many commuters struggling to get to work on other overcrowded lines of the Tube.

The British government has awarded contracts to a number of private companies to upgrade the Tube but union leaders have opposed the part-privatisation drive.