SAN FRANCISCO (CBS SF) — A debris fire in the Transbay Tube caused BART to single track trains between San Francisco and the East Bay, causing major delays during peak commute time, BART officials said Tuesday.

BART was forced to shut down power to both sides of the third rail due to the fire. The incident caused BART to single track trains in the tube for nearly an hour.

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Crowds at Embarcadero during Transbay Tube shutdown (Carlos Castaneda)

BART officials said they were investigating reports of sparks in the ventilation system on the Oakland side along with the Oakland Fire Department.

The Transbay Tube was reopened fully at 5:55 p.m., but BART said to expect major delays.

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Passengers on social media were saying that they were on stuck trains and crowds at San Francisco BART stations were packed.

BART said AC Transit is offering mutual aid from the Transbay Terminal to 20th and Broadway in Oakland via the NL Bus.

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The NL will connect riders from the Salesforce Transit Center in San Francisco with the 19th Street BART station in Downtown Oakland. Muni is providing mutual aid for commuters traveling to the Peninsula.