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A stray balloon may be behind a delay in train services on the Mandurah and Joondalup lines this morning.

Train services on both lines came to a halt for around 10 minutes just after 8am after reports of a fallen power cable at Perth Underground Station.

Passengers were reportedly evacuated from the platform after the fallen wire began sparking.

PTA spokesman David Hynes said the delay had been triggered by a minor problem with an insulator.

"We suspect it might have been a child's balloon, but that's being investigated," he said.

Passengers on the Mandurah line experienced the longest delays.

Both lines have experienced issues in recent months, with New Year's Eve services on the Mandurah line delayed after cables at Murdoch Station overheated.

While thousands of commuters were left stranded last October after overhead cables became tangled on a moving train and snapped.