Two men have been arrested and two are on the run after a series of home invasions, car jackings and a high-speed crash in Sydney's south-west.

Key points: Four balaclava-clad men are alleged to have taken part in home invasions, car theft and a high-speed car crash

Four balaclava-clad men are alleged to have taken part in home invasions, car theft and a high-speed car crash Two were arrested and one of them taken to hospital after a police operation

Two were arrested and one of them taken to hospital after a police operation People are warned not to approach a yellow Holden Commodore, allegedly stolen from Moorebank

A large-scale police operation was sparked by the incidents, which began at 7:00am when four men wearing balaclavas broke into a home in Fairfield.

Chief Inspector Greg Tetley said police were still searching for two of the four men.

"Their behaviour is very dangerous, a lot of people were very scared, a lot of people were put in danger on the motorways and at [their] homes," he said.

Stolen car in fiery Moorebank crash

A woman was assaulted in the house and a man living in a granny flat was assaulted with an iron bar.

They were taken to hospital for treatment.

The assailants fled in a white Mercedes and at 8:45am in Bonnyrigg the four men carried out a second home invasion.

Two of the men were carrying firearms and it is alleged a round was discharged in the house during the confrontation, but no-one was injured, according to police.

A short time later, a Mercedes driven at speeds of up to 200 kilometres per hour was seen on the M5 at Moorebank.

It crashed into another car and caught alight near the Moorebank Avenue off-ramp.

Men are armed and dangerous

Four men wearing balaclavas got out and ran away on foot.

A short time later, a grey Nissan Navara 4WD was carjacked by two of them, but it was abandoned a short time later at a service station in Moorebank.

The two then carjacked a yellow Holden Commodore, with NSW registration plates DAN-359, and are still on the run.

Police have urged members of the public to call triple zero, but not to approach the Commodore, with the two men considered armed and dangerous.

"At this stage we've got detectives from Fairfield and Liverpool and we're being assisted by the state crime command robbery and serious crime squad," Chief Inspector Tetley said.

He said many resources were involved in the arrest of the two who were on foot.

"We had the police airwing, a number of police dog squads searching for the offenders on foot," he said.

"Police set up a perimeter to try and contain the offenders and keep the members of the public safe and we were able to arrest those offenders inside the perimeter."

One man was found on the roof of a home on Grevillea Crescent, Prestons, the other at a school on Kurrajong Road.

The man on the roof was taken to hospital but his condition is unknown.