SAN FRANCISCO (CBS SF) — Heavy overnight rainfall likely caused a 20-by-30-foot hole sinkhole still growing in the Bay Area Wednesday morning.

San Francisco Public Utilities Commission responded to a report of a sinkhole at Sixth Avenue and Lake Street at 9:17 a.m. Traffic was unable to pass between Fifth and Sixth streets.

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SFPUC spokeswoman Jean Walsh said sand had eroded around a water main pipe at the intersection, leaving the pipe exposed. At some point Wednesday morning, the pipe collapsed, causing more sand and rocks to erode.

Later investigation reported rain had weakened the soil under a century-old water main that had survived the 1906 earthquake. It was built in 1905, but the storm overnight was finally too much for its brittle walls.

Walsh said residences located within two blocks of the area are without water as crews work to repair the water main, which could take several hours.

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Crews will work on the ruptured storm drain tonight and will likely work on road reconstruction on Thursday, Walsh said.

Earlier, cars traveling westbound on the Bay Bridge tried to avoid a 2-foot-wide pothole in a lane just before the Treasure Island tunnel. Caltrans previously closed two lanes to make the repairs.

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