– A two-day strike by London Underground employees over job cuts and ticket-office closures caused travel chaos in the capital as stations remained shuttered and roads struggled to cope with extra demand.

The Tube, which usually carries more than 3.3 million people on weekdays, began running later than usual, with two lines and more than 40 stations completely closed, Transport for London said on its website. Frequencies on routes that remained open dropped to as low as one train every 20 minutes, and buses filled quickly, leaving some passengers stranded.

Unions called the strike over Mayor Boris Johnson's plans to scrap ticket booths with the loss of than 750 jobs, spurred by the introduction of Oyster travel cards that automatically open gates after being charged with credit. Labor leaders say that while less than 3 percent of journeys involve a visit to a booth, staffing stations is vital to guaranteeing public safety.

"The action is rock solid this morning and has reduced the network to a skeleton service with only a few ghost trains running through closed stations," said Bob Crow, general secretary of the Rail, Maritime & Transport union.

The Waterloo & City Line, which carries commuters from Britain's busiest railway station to the heart of the financial district, is closed for the duration of the strike, together with the Circle Line that rings the center of London. Stations on the Piccadilly Line and Central Line are open only at their eastward and westward extremities.

While the Northern Line, the system's busiest, is operating a "good service," according to TfL, which oversees the Tube, northbound trains didn't start until 7:30 a.m., 30 minutes later than planned, causing a crowd of about 500 people to gather outside Morden station at its southern end.

Commuters were later shepherded by police to platforms, where an absence of indicator boards led to confusion over whether trains were bound for the City or a branch serving the West End and caused many to dash between carriages.

Crow said that Prime Minister David Cameron's Conservatives were "playing politics" and should compel the mayor to honor an election pledge not to shutter ticket offices.

Johnson's plan would retain ticket offices at five central Tube stations plus Heathrow. Unions are also concerned that a study of the viability of driverless trains could lead to elimination of many more jobs.