Londoners were forced to take buses, boats and taxis to work as a strike by subway workers crippled service.

About 40% of London's subway trains ran this morning, with one line completely out of service, Bloomberg News reported. The city added about 100 extra buses and a boat with room for 500 people to help alleviate traffic congestion.

Many subway workers ceased work yesterday in the fourth strike since 2002. The strike is due to last 24 hours, and there are no scheduled talks between Transport for London and unions representing the striking workers.

"It was a nightmare," Alain Portmann, who works at an online advertising agency, said after his journey to work took 2 ½ hours instead of the usual 35 minutes "With the amount of traffic, people were just getting off the bus and saying they were going to walk."

A single subway journey in central London costs £4 (about $6.12) if you pay cash, compared with $2.25 on the New York City subway.