Busy Harvard Square was shut down for nearly three hours Friday night after a gasoline truck sideswiped a taxicab and began to leak its easily combustible fuel.

The Sunoco Ultra 94 truck had turned onto Brattle Street when it clipped the cab.

The accident caused a valve on the truck to open and gasoline began to seep out.

The valve is self-sealing, but was not able to fully stop the leak, said Cambridge Fire Department (CFD) Deputy Chief Frank Murphy Sr.

The CFD's Hazardous Materials unit arrived at the scene moments later with several other fire trucks.

Police officers and firefighters in full protective masks began to seal off the area.

"If we have a fire here now, everyone is as good as dead," a firefighter said while encouraging passersby and onlookers to extinguish their cigarettes.

The Clean Harbors Environmental Services company responded to clean the spill, which was supervised by the Massachusetts Department of Environmental Protection.

Workers spread the absorbant chemical known as "Speedy Dry" along the road and sidewalks.

Gas lines running along several buildings on Brattle Street were shut down while firefighters checked the basements for any leaks.

As a precaution, the MBTA stopped all Red Line trains--both inbound and outbound--for several hours while the leak was cleaned up.

Two other empty gasoline trucks arrived andpumped nearly 2000 gallons from the disabled truckinto their tanks.

The gas leak forced many Square shops to closeearly on their busiest night of the week.

"We're losing business," said an employee atOut of Town News.

Police re-routed traffic around the Square asfar north as Church Street and Mass. Ave.

--Courtney A. Coursey and Matthew W. Granadecontributed to the reporting of this article.