A pregnant woman was among several people held up by armed robbers who targeted a bank and golf club in Sydney's south-west.

Police have set up a strike force to investigate the robberies as they continue to search for four suspects, who remain on the run after crashing their getaway car and unsuccessfully attempting to hijack others.

Four streets in the suburb of Fairfield were evacuated as more than 100 officers searched for the suspects, who were armed with guns and a hammer and wearing balaclavas.

The crime spree began when the men attempted to rob the Commonwealth Bank on Waldron Road in Chester Hill at 10:40am (AEDT).

The ABC understands several employees were inside the bank at the time, including a pregnant woman.

After their robbery attempt failed, the men went to the Rosnay Golf Club at Auburn where they threatened staff and stole money from a cash register.

Local police in an unmarked car spotted the men and gave chase, but the pursuit was called off after about three minutes when the suspects' car collided with another car at Villawood.

The female driver of the car was not injured, police said.

Police have locked down streets in Fairfield as they hunt for the armed robbers. ( ABC News: Tahmina Ansari )

Police said the suspects tried to hijack two other cars before fleeing on foot through Hercules Street at Fairfield, where they reportedly ran through a house and jumped a fence.

Heavily armed officers evacuated homes and surrounded the area, alarming some residents.

Sorry, this video has expired Armed robbers target Sydney bank and golf club ( Lucy Carter )

Andrew Vilches said the police surrounded the house he was in with their guns drawn.

"About 15 minutes later, the cops started to come in their big vests and I thought, oh no," he said.

"A couple of minutes after that they told us to leave the house.

"I asked them what was going on and they said, 'I can't tell you'."

Hercules, Tangerine, Mitchell and Crown streets were all in lockdown.

Residents were later allowed to return to their homes, and police called off the search about 3:00pm.

Bank staff shaken but unhurt after robbery attempt

The mother of a pregnant bank worker, who did not want to be identified, said she came to the scene straight after her daughter phoned to tell her about the robbery.

"She was very shaken, very, very shaken and emotional," she said.

"She's pregnant and I was really worried about her and the baby... but they're OK.

"She just wanted to let me know that she was OK and I've just come down here just to make sure she's fine.

"It was the worst feeling ever knowing that your daughter could have been killed instantly."

The Commonwealth bank on Waldron Road in Chester Hill was held up about 10:40am (AEDT). ( ABC News )

Superintendent Peter Gilham said the men were considered dangerous.

"We believe they're armed. They may still be armed," he said.

"Obviously, they're to be treated as such, so if anybody sees anything suspicious, we ask them to ring the local police or Crime Stoppers straightaway."

Detectives from State Crime Command's Robbery and Serious Crime Squad have established Strike Force Wallent to investigate.