A large sinkhole has prompted the closure of two blocks in South San Francisco, possibly through tonight, public works superintendent Gary Batis said.

Public works employees spotted a small dent in the roadway at Magnolia and Baden avenues Monday and drilled it to determine what was underneath, according to Batis.

What they found was an 18-inch storm drain that had broken and sucked in the soil, creating a void beneath the asphalt, Batis said.

The workers secured the site until this morning when they returned to open the 5-foot by 10-foot sinkhole and repair it.

Magnolia Avenue has been closed between Baden and Commercial avenues until the sinkhole is fixed, Batis said.