Millions of Londoners faced a grim commute Wednesday, taking boats, buses and bicycles or walking in the rain as a strike by subway workers crippled the city's subway system.

It was the most disruptive strike on the Underground system since September 2007, when a walkout also shut down most of the capital's Tube.

Mayor Boris Johnson said the walkout was causing huge disruption and urged union leaders to return to talks aimed at resolving disputes over pay, disciplinary issues and job losses.

The Rail, Maritime and Transport union, which represents thousands of drivers, station staff and maintenance workers, ordered members to walk out late Tuesday after last-minute talks broke down. The strike is due to last until Thursday evening.

Every day, about 3.5 million people use London's 249 mile- (402 kilometer-) long Underground.

Nine of the city's 11 subway lines were fully or partly closed Wednesday, prompting commuters to crowd onto buses, walk down ramps to boats along the River Thames, or cycle to their offices. Business groups said some people would simply be unable to get to work.

Among many commuters, Londoners' famous patience was wearing thin.

"I don't really know where I am, where I'm going or how I am going to get back," said management consultant Steven McCartney, 38, as he studied a bus map in west London.

"This is an essential service, the Tube is, and service shouldn't ever be stopped by a strike like this. Do they not see the harm and the pain that it's causing this city today?"

The London Chamber of Commerce estimated the strike could cost as much as 100 million pounds ($164 million) in lost productivity.

The union accused Underground management of scuppering a last-minute deal to avert the strike. But Johnson said the walkout was "unnecessary and misery-making" for commuters.

"The two sides are extremely close — it is essential that people of goodwill get around the negotiating table," he said.

Regular service isn't expected to resume until after 7 p.m. (1800 GMT, 2 p.m. EDT) Thursday, unless a compromise can be reached.

Bettina Vogel, a 34-year-old advertising account director, said the strike proved how much Londoners rely on the Tube.

"I had to take the train and a bus, and that took two hours versus 45 minutes," Vogel said. "It's very inconvenient, but it's definitely sending a message, because we realize how dependent we are."

Charlotte Tibbs, a 24-year-old assistant retail manager, said her usual 45-minute subway journey had taken two hours by bus.

"I have to phone my boss to say I'm going to be late," she said.

The walkout also was expected to frustrate thousands of fans traveling to north London's Wembley Stadium for England's World Cup qualifying soccer match against Andorra on Wednesday.