The Oakland Fire Department is assisting BART in evacuating the train, BART spokesman Linton Johnson said.
The incident was reported at 10:30 a.m.
The train, which was headed to Richmond, is stuck in a tunnel between the two stations, Johnson said. Fire crews are helping to evacuate passengers, walking them through the tunnel to the 12th Street station.
"Trains go very slowly through that area, so we don't anticipate there will be any injuries," he said.
The incident has caused only minor service disruptions so far, Johnson said shortly before 11 a.m.
BART has numerous trackways and tunnels in the area, he said, and there are many options for routing trains. Johnson said passengers coming from San Francisco may experience minor delays.