BART officials say Hayward Fire Dept has requested they close the station and power off the tracks because of a fire and downed PG&E power lines nearby.
At one point trains were turning back at Hayward and Union City.
The station was reopened around 6:20 pm, but there are "major delays" in the Warm Springs, Richmond and Daly City directions.
Parallel bus service is available on AC Transit bus #99 between Union City, Hayward and South Hayward stations.
Stay with ABC7 News for the latest details on this developing story.