Flames between some lovers were prematurely quenched yesterday as firefighters extinguished an underground blaze that forced the evacuation of several restaurants and businesses on Brattle Street.

A fire in the street’s sewers blew the covers off of three manholes, causing the street to be cordoned off from Massachusetts Avenue to Palmer Street and forcing about a dozen local businesses to be evacuated, according to Deputy Fire Chief James F. Burns. Firemen were summoned to the scene after black smoke and flames were seen shooting up from the manholes. Several fire trucks and ambulances arrived, completely blockading the area. Policemen directed traffic and curious bystanders away from the firefighters as they battled the subterranean flames.

As of last night, the City of Cambridge Fire Department had not determined the source and extent of the fire, Burns said. The fire was successfully quenched and an investigation is underway. Among the businesses closed and evacuated was the Brattle Street Theatre, which had been running a special Valentine’s Day showing of “Casablanca.”

The fire claimed no casualties, except perhaps the nights of a few steamed-up couples.

—Staff writer Jamison A. Hill can be reached at jahill@fas.harvard.edu.