A century-old tunnel that connects motorists to different parts of Point Richmond has been shut down after crews discovered concrete failure, city officials said.

Crews from TPA Construction, which is working on an improvement project on the Dornan Drive Tunnel, found Friday that part of the tunnel's upper interior had failed, causing large chunks of concrete to fall to the ground, according to a statement from the city's engineering department.

Further inspection revealed a large attic-like void measuring about 12 by 10 feet between the tunnel's interior concrete lining and the ceiling, and that parts of the lining had thinned to as little as 4 inches thick, according to the city.

After an assessment by the city's project engineers, The Crosby Group, the city quickly shut down the tunnel, which links commercial areas of Point Richmond to the Brickyard Cove and Seacliff neighborhoods and to the shoreline area that includes Keller Beach Park.

Melissa Tigbao, staff engineer for the city, said the tunnel would be closed until repairs to the concrete are completed -- hopefully by April 30, she said.

"It will inconvenience bicyclists, motorists and pedestrians, but there are other ways to get around," Tigbao said. "It really is a safety reason."

Motorists can now access Point Richmond's commercial areas from the Brickyard and Seacliff neighborhoods or from Keller Beach Park via a detour along Washington Avenue to Western Drive.

Those areas can also be accessed through Canal Boulevard and Seacliff Drive.

Construction crews began work on the 100-year-old tunnel last month to repair cracked areas of the concrete lining and to install a new drainage system, according to city officials.