Two small sinkholes swallowed a piece of 15th Avenue in the Richmond district Sunday, forcing the closure of the roadway between Geary Boulevard and Clement Street.

The San Francisco Public Utilities Commission blamed it on a collapsed 100-year-old sewer main.

One sinkhole, about 2 feet wide, opened Sunday morning in the middle of the street, and another appeared on the verge of opening a short distance away. Vehicles parked in the area were not affected.

Construction crews had already been working on 15th Avenue, and that portion of the roadway was quickly closed to traffic. The SFPUC expected it to reopen late Sunday.

The SFPUC said the aging sewer line was scheduled to be replaced this month as part of the agency’s multibillion-dollar program to upgrade The City’s sewer system.