A major bridge in the San Francisco Bay Area has been closed after large chunks of concrete fell from the upper deck.

The San Francisco Chronicle reported that one car was damaged but no injuries were reported.

The California Highway Patrol posted an alert about the Richmond-San Rafael bridge closure shortly before noon on Thursday, saying there was no estimated time for reopening.

It was not clear what caused the concrete to fall. A CHP spokesman did not immediately return a call seeking more information.

The CHP posted photographs showing what appeared to be football-sized pieces of concrete that had fallen. The agency said it was working with Caltrans to determine the problem and find a solution.

The closure was expected to cause heavy traffic.

A California Highway Patrol officer drives on the closed Richmond-San Rafael bridge Thursday, Feb. 7, 2019, in Richmond, Calif. (AP Photo/Ben Margot
A California Highway Patrol officer drives on the closed Richmond-San Rafael bridge Thursday, Feb. 7, 2019, in Richmond, Calif. (AP Photo/Ben Margot
Standstill traffic on westbound Interstate 580 backs up due to the closure of the Richmond-San Rafael bridge Thursday, Feb. (AP Photo/Ben Margot)
Standstill traffic on westbound Interstate 580 backs up due to the closure of the Richmond-San Rafael bridge Thursday, Feb. (AP Photo/Ben Margot)
This photo released by the California Highway Patrol Marin shows damage to concrete on the Richmond-San Rafael Bridge near Richmond, Calif. (California Highway Patrol Marin via AP)
This photo released by the California Highway Patrol Marin shows damage to concrete on the Richmond-San Rafael Bridge near Richmond, Calif. (California Highway Patrol Marin via AP)
The roadway is empty along the Richmond-San Rafael bridge looking westbound from the toll plaza, Thursday, Feb. (AP Photo/Ben Margot)
The roadway is empty along the Richmond-San Rafael bridge looking westbound from the toll plaza, Thursday, Feb. (AP Photo/Ben Margot)
The roadway is empty along the Richmond-San Rafael bridge looking westbound from the toll plaza, Thursday, Feb. (AP Photo/Ben Margot)
The roadway is empty along the Richmond-San Rafael bridge looking westbound from the toll plaza, Thursday, Feb. (AP Photo/Ben Margot)