Hundreds of Perth-bound commuters were stranded on a train outside the East Perth station when it stopped unexpectedly this morning.
The train, which was packed, came to a halt about 8:00 am when its power was cut.
The Public Transport Authority says it is not clear what caused the electrical fault.
The PTA's David Hynes says normally the train would have been pushed to the next station but once passengers started getting off, it became unsafe to do so and caused further delays.
"The driver had lost power and he lost communications as well which meant that he couldn't send a message to the passengers," he said.
"The passengers, for whatever reason, forced some of the doors open and started exiting the train which is something we would prefer didn't happen."
Passengers had to wait at East Perth station for replacement services.
One commuter Christabel says it was the second delay on the Midland line in as many weeks.
"I think it's just terrible," she said.
"Last week it happened too that we were delayed and sometimes we're just delayed half way through, on the way in, sometimes on the way out."
Mr Hynes says the incident is not related to overnight rain or previous incidents on the same line.
"It would seem to have been a problem with the train rather than the overheads or the power itself, it was a problem with the train," he said.
The train blocked the line for about an hour, causing delays to the Midland service for some time.