Commuter chaos after 'overheight vehicle' shut Sydney Harbour Tunnel during peak hour

Sydney 's morning commute has been thrown into chaos following a shutdown at the Sydney Harbour Tunnel.

An overheight vehicle closed down all southbound lanes just before 7am, Live Traffic Sydney reported.

The tunnel reopened a short time later, but traffic is already banked up across North Sydney.

Radio station 2GB reports traffic is now queued about 8km into the Lane Cove tunnel further north.

The truck that closed the tunnel lanes has been moved to the side and heavy vehicle inspectors are now on site.

'If you can delay your journey into the city, you would be wise to do so,' 2GB host Ben Fordham said.

Motorists are advised to use the Harbour Bridge as an alternative and allow for extra travel time, and to 'exercise caution and allow some extra time' if going for the tunnel.