Up to 300 passengers are stranded on a train near Sydney's Strathfield station after a high-voltage power cable came down on top of carriages.
Train services on most lines running between Sydney's Central Station and Lidcombe have been halted, with only the southern T4 line running normally.
Sydney Trains said it was working to isolate the overhead 15,000-volt wiring.
Howard Collins, coordinator general of Transport for NSW, said crews needed to shut off the power cable before attempting to remove the passengers from the affected train to the nearest station.
"The power connection device on the train has collided with a number of wires, the overhead wire system," he explained at a press conference on Tuesday afternoon.
A short time after he spoke, people could be seen emerging from the train.
Cause of train incident remains uncertain
It is still not clear what caused the live wire to come down on the carriage.
"We'll find out why this incident occurred … it is too early to say was it the rain, or is it something to do with the overhead wiring system or has there been something else that has got caught up in the overhead wire itself," Mr Collins said.
CCTV and computer diagnostics will help Transport for NSW understand how a "catastrophic event of this nature" occurred, he added.
"The priority is getting those people off the train."
Mr Collins said rideshare service Uber had agreed to price cap.
"I'd ask customers and passengers to be aware if you're not travelling please do not do so on the rail network."
It is still not clear what caused the live wire to come down on the carriage.
Buses are being brought in to replace services later in the evening but major delays will continue across the network.
