Auckland commuters are being warned to expect major delays as four motorways are badly congested after a truck struck a bridge on the Southern Motorway this afternoon.

Motorists are facing hour-long commutes over an 8km stretch of the Southern Motorway after the truck crash blocked several southbound lanes when it struck the Penrose Bridge.

On the Southwestern Motorway, meanwhile, there is start-stop traffic southbound between Onehunga and Manukau and between Maioro St and Hillsborough.

Westbound lanes on the Northwestern Motorway are also in the grips of heavy traffic between the Waterview interchange and the Lincoln Rd off-ramp.

The westbound lane on Penrose Bridge, just after the Ellerslie-Panmure Highway, has also closed to traffic after the collision.

The bridge’s eastbound lane is being managed by stop/go signs.

The gridlock has extended from the Southern Motorway at Spaghetti Junction and onto the southbound lanes on the Northern Motorway to the Fanshawe St off-ramp.

City-bound lanes on the Northwestern Motorway also have major delays as the congestion creeps along on-ramps onto the Southern.

Traffic has also started building on the central city’s Hobson St as cars struggle to get through the intersection onto the Southern on-ramp.

Rubberneckers in the northbound lane of State Highway 1 are exacerbating the traffic, creating congestion back to Ōtāhuhu.

Buses have also been delayed, several stops closed and three bus routes diverted.

Waka Kotahi NZTA alerted the crash, on SH1, at 2.25pm.

Motorists caught in the chaos have told the Herald the Southern Motorway was “gridlocked”.

Two lanes on SH1 have been closed and contractors were on scene inspecting the bridge for damage.

The transport agency warned motorists to expect delays and to pass the crash with care.

Live traffic data shows a snaking line of bumper-to-bumper traffic southbound on the motorway from Mt Wellington to the city.

Police have been approached for comment.