The NSW Ambulance service has apologised after it took at least 45 minutes to respond to an alleged hit-and-run collision that killed a woman in Sydney's west.

Shahrazad Rahman, 39, of Merrylands, was struck by a car on Rawson Road in Guildford about 9.15pm on Saturday.

She was given CPR by police and bystanders but died on her way to Westmead Hospital.

Fairfax Media understands the ambulance service received calls to Rawson Road at 9.20pm, 9.43pm and 9.55pm.

"NSW Ambulance extends its sincere apologies and condolences to the family of this patient," it said in a statement.