A four-vehicle accident on the M4 at Auburn in Sydney's west is causing significant delays.

The road is closed citybound between James Ruse Drive and Silverwater Road, with diversions in place.Delays of up to seven kilometres have been reported.Drivers are being advised to avoid the area.In a separate incident on the New South Wales mid-north coast, there are 4 kilometre-long tailbacks at Bulahdelah after an accident.The Pacific Highway is closed northbound with diversions for some vehicles.