Hundreds of Sydney commuters have endured peak-hour chaos after a power issue brought the city’s train network to a standstill.

The disruption on Australia’s busiest suburban network was triggered when a live overhead wire came down onto the roof of a train about 2.30pm on Tuesday, trapping passengers on board, cutting power and causing widespread delays.

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NSW Transport Minister John Graham described the situation as dangerous, saying a 1500-volt power connector was sitting on top of the train carrying 300 passengers about 20 metres from Strathfield station.

“This is a very serious incident, right in the heart of Sydney’s train network,” Graham told ABC News.

Transport for NSW urged passengers travelling on the T1, T2, T3, T8, T9 lines, as well as Central Coast & Newcastle Line and Blue Mountains Line, to allow extra travel time, delay their journey, or seek alternative transport options.

Co-ordinator General Howard Collins confirmed that only one line was unaffected.

“The only area not affected by this is the T4 South Coast and Central services. The rest of the other lines, including the airport line and other services on the North Shore, are impacted by this significant delay,” Collins said.

Transport for NSW activated its agreement with Uber to prevent unreasonable surge pricing during the incident and its flow-on effects.

Train platforms were overwhelmed with commuters stuck due to delays, with two trains stuck on the tracks.

A commuter told 7NEWS he had been trapped in a train carriage for almost three hours without air conditioning.

“We had a sudden turn or something like that, and then the train stopped all of a sudden and the lights went off — it was not bright as it usually is,” Bishal Dangi said.

“It’s suffocating. All of the people are asked looking for answers.”

But Dangi couldn’t leave the train.

“They said they were going to disembark us,” he said. “OK, at least if you could do that, I could get to work on time. I could take an Uber or something. I have no option. I can’t get off. There’s nowhere to go.”

While passengers are reported to be safe, they couldn’t be evacuated until the live wire was safely isolated.

“The power is off, but we do not want anyone to be getting off that train as the overhead live wire is sitting on the roof of the train at the moment,” Collins said.

“Engineers are going on site, putting earthing bonds, as we call it, on, operating the isolating switches, and as soon as that occurs, we will get people off this train.

“But the safest place to be, at the moment, is to remain in the train and not on the track or touching the outside of the train.”

Collins apologised for the lengthy process, and stressed the seriousness of the situation.

“If you get very near or touch wires with that amount of voltage and amperage, it will kill you straight away.”

Collins said he hoped services would be back up and running by Tuesday night, but authorities have warned it could even affect Wednesday’s morning commute.

“We are aware this will cause major problems and delays. We are advising in the morning to make sure you check the latest information,” Graham said.

“It’s possible there could be some knock-on effects.”

The metro, light rail and local buses are not impacted.

“About a million people rely on public transport to move around the city,” Graham said.

“This is a big impact, the rail network is crucial. It’s greatly assisted by the bus and metro network.

“The fact they are running is making it easier tonight.”

- With AAP