7pm: Heavy traffic has cleared on Mount Ousley Road, however motorists are now experiencing delays further north.
Heavy holiday traffic is affecting the M1 Princes Motorway from Helensburgh to Heathcote, according to Live Traffic.
Earlier: Four cars have been caught up in a nose-to-tail series of crashes that are causing delays on Mount Ousley Road.
The crash occurred in the northbound lanes at the top of the mountain, a short distance south of the Picton Road turnoff, about 5pm on Monday.
Read more: Bulli Pass open for long weekend
Eleven people have suffered minor injuries, but all have since removed themselves from their cars.
Three of the cars involved have been badly damaged.
Police and NSW Ambulance paramedics are on site and are continuing to assess the injured. None are expected to require transport to hospital.
The Mercury understands the crashes have caused a significant build-up of traffic, reaching almost to the bottom of the mountain.
Roads and Maritime Services is monitoring the crash site.
Motorists are advised to avoid the area, if possible.
Bulli Pass remains open until 9am Tuesday .
More to come.