San Francisco  - The Bay Bridge into San Francisco is expected to remain off limits to traffic this week after a potentially dangerous crack was discovered during a maintenance closure.

The bridge has been closed since Thursday for a weekend project to upgrade earthquake safety on the span linking San Francisco with Oakland.

Traffic had been scheduled to resume on Tuesday morning, after Monday's US observance of Labour Day. But on Saturday, inspectors discovered a significant crack in a steel link undergirds the eastern side of the bridge.

Built 73 years ago, the Bay Bridge was repaired after suffering severe damage in a 1989 earthquake. (dpa)