The men were contaminated at a building site and made their own way to the hospital, where staff contacted emergency services.

In a statement, Westmead Hospital said the men arrived in the emergency department at around 4pm and were receiving treatment.

"All patients are in a stable condition," a spokeswoman said.

"Fire & Rescue NSW has established a decontamination zone in the hospital's ambulance bay as per HAZMAT requirements.

"Westmead Hospital will continue to receive other patients via ambulance. There is no risk to other patients, staff or visitors."

Staff at the hospital were sent a message on their phones which read: "Disaster".

Superintendent Ian Krimmer from Fire and Rescue NSW said four crews were called to the hospital, including one HAZMAT crew, to decontaminate workers who were coming in.

"It appears as though they may have been working at the old Rosehill Oil Refinery, demolishing something, possibly contaminating them," Mr Krimmer said.

"We were decontaminating them as they were going in [to the hospital]."

Vision from the scene showed firefighters in bright orange overalls, wearing oxygen tanks, standing outside the entrance to the emergency department.

A tent and tarpaulin were set up in the car park as the decontamination took place.

Westmead Hospital said it would provide an update on the Western Sydney Local Health District Facebook page once normal services resumed.

A NSW Ambulance spokeswoman said paramedics were on standby at the hospital.

with Roydon Ng

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