A high-voltage power line has fallen on several homes and roads at Plumpton in Sydney's west, trapping residents in their homes.

Key points: The power line is draped across homes and roads in the area

The power line is draped across homes and roads in the area It is also sagging over the M7, where speed limits have been lowered

It is also sagging over the M7, where speed limits have been lowered Power to homes in the area has not been affected

The area has now been declared secure after the line fell between two large steel towers.

NSW Fire and Rescue Inspector Bob Mey said crews were initially called to a fire in the area about 7:00am.

"Our crews then noticed a high-powered line had fallen down on the house and probably caused the fire," he said.

"We then saw the line had fallen across many laneways, backyards, carports and cycleways in the area."

Resident Mario Davaro said he had been asleep when he heard an explosion and realised his house was burning.

"The [electricity] line contacted the gas line and it just blew — the side of the house was on fire," Mr Davaro said.

"It was such a shock, it was an adrenaline rush really, trying to call the fire brigade.

"They were here within two minutes."

Russ Gazitepe said he heard a bang and thought there had been a car accident on the street when emergency vehicles arrived.

"All of a sudden they found a cable on my car, my carport — thank God no lives were lost," he said.

"They told me it was a 100,000 watts this one, which is scary."

John Lyons said he was stuck in his house for 30 minutes, with a police helicopter buzzing overhead.

Asked if he should go out and buy a lottery ticket, Mr Lyons replied: "I already have one, I'll probably check it today, no-one was hurt."

One road in leaves residents 'trapped'

Affected streets included Aquilina Drive, Beverly Place, Tilden Place, Polonia Avenue, Carroll Crescent, and other surrounding streets in the Plumpton area.

Inspector Mey said the residents were effectively trapped.

"There is only one road in and out of the area," he said.

"With the line on the road, residents are not able to leave their homes."

The power line fell on homes in the area. ( ABC News: Meredith Griffiths )

The fallen power line caused problems on the nearby M7, with a high-voltage power line sagging over the motorway.

Residents in the affected streets were advised to stay in their homes and, as a precaution, anyone near fallen power lines should stay 8 metres away.

"We believe the line has broken in the middle, but our main concern at the moment is to make the area safe," Inspector Mey said.

Endeavour Energy regional manager Drew Ferguson said the safety of residents was paramount, while emergency crews worked to repair the 132kV line.

Mr Ferguson said a lightning storm with strong winds last night could be to blame but a team would investigate the cause behind the line failure.

"It's highly unusual for a transmission line to fail and often extreme weather events can be a contributing factor," he said.

"We are also working with Roads and Maritime Services to re-tension the line across the M7 near Woodstock Road.

Motorists were being advised to slow down to 60kph in the area as work was safely completed.

Power to homes in the area was not affected.