Marin County officials said Friday that 2.7 million gallons of sewage has spilled into San Francisco Bay.

The spill occurred Thursday night in Richardson Bay, an arm of San Francisco Bay that stretches between Tiburon and Sausalito in Marin County.

The extent of the spill's spread is as yet unknown.

"An accidental release of partially treated sewage and storm water occurred at a sewage treatment facility operated by the Sewerage Agency of Southern Marin," the county said in a press release.

The spill happened when a pump at the water treatment plant failed, as did an alarm that's supposed to alert officials of any problems, according to county officials.

The water near the site is currently being tested. Heath and environmental authorities are warning the public to avoid contact with bay water or sport fishing in the area until further notice, the county said.