Wet weather and twice the usual number of morning accidents are causing significant delays for Sydney drivers today.

"There have been more than 40 incidents, mainly minor crashes and breakdowns, and this is twice as many as we would expect in a morning," an RTA spokesman said.

Traffic was banked up to the start of the Anzac Bridge from the west about 10am and was very heavy on Victoria Road.

A bus broke down on the Harbour Bridge about 8am, causing two northbound bridge lanes to shut. The bus was cleared from the bridge and the lanes were reopened, but traffic on and near the bridge remained heavy.

The breakdown had not affected traffic on the southbound lanes of the Harbour Bridge, but the wet weather was having an impact on traffic across the city, the RTA said.

A car breakdown at Naremburn also led to heavy traffic in the area.

There were also significant delays entering Harris Street, Pyrmont, from the Western Distributor.

Earlier today a bus breakdown on Bridge Street in the CBD and car breakdowns at Strathfield, Cremorne, Granville, Leppington and in the airport tunnel at Mascot caused significant disruptions.

The RTA advises drivers to reduce speed and exercise caution at accident sites in Newtown, Concord and Cammeray.

At 6.50am there was a car accident on the Harbour Bridge affecting two lanes northbound, but it was cleared soon after.

Earlier today there were accidents in Maroubra, Arncliffe, Windsor, Warwick Farm, Mooney Mooney, Epping, Rosebery, Dundas, Chatswood, Kensington, Northmead, Granville, Padstow, Asquith, Eastern Creek and Auburn.

Traffic lights were also blacked out on Beecroft Road at Cheltenham and at Pennant Hills at 10.50am, affecting traffic in both directions.

The Bureau of Meteorology issued an alert this morning advising motorists to take care because of wet slippery conditions with rain and showers this morning.

- with Arjun Ramachandran