The downtown Berkeley Bay Area Rapid Transit station was closed because of the power failure, the agency said in a tweet. The agency later said it had a backup generator to provide power to the station.

Jenny Wong, Berkeley’s elected city auditor, said she had noticed the power was out around 8 a.m. and had gone for a walk with her husband to see how the South Berkeley neighborhood was faring. Ms. Wong said she had noticed that the traffic lights were not working and many businesses were open but unlit.

“It was very calm,” she said. “I just felt really bad for folks working at a small market we passed. The employees were standing outside because they can’t do business when this happens.”

Barnali Ghosh, a North Berkeley resident, said she had noticed her internet was not working when she woke up. After her lights did not turn on, she called the power company.