Man causes traffic chaos after he climbs the Sydney Harbour Bridge

An unauthorised man has climbed the Sydney Harbour Bridge bringing early morning traffic to a standstill

A man who climbed the Sydney Harbour Bridge this morning, sparking a major police operation lasting five hours and sending traffic into chaos, has been handcuffed by authorities and brought down.

Police rescue officers followed the man on to the structure but it was proving hard reach him because he kept moving, a NSW Police spokeswoman said.

Three of the four northbound lanes of the bridge are closed.

The man reportedly rode his bike to the bridge and began his climb at 4 a.m. local time.

It is still unclear as to why the man climbed the bridge. Lengthy traffic jams both sides of the bridge.

"Due to the ongoing police operation on the Sydney Harbour Bridge, be aware it may be necessary to close lanes at short notice - please observe and obey all traffic signs and directions", NSW Police tweeted.

The 44-year-old climber was described as "distressed and rambling", when officers finally convinced him to walk back down, Network Ten reports. Those already travelling might not have much warning, but if you know of anyone heading in across the bridge, perhaps try and call them and let them know to use the Sydney Harbour Tunnel or cross at Gladesville instead.

Drivers were advised to avoid the area.

Climbing the Sydney Harbour Bridge is illegal unless authorised.