• Police confirm the Southern Motorway is now open
• Motorists advised to take care as there is still a backlog of traffic in the area.
7:00pm: Don't forget that part of the Southern Motorway, southbound will be closed overnight, for emergency repairs due to the damage caused by today's accident.
The motorway southbound will be closed between Ellerslie and the south eastern arterial southbound from tonight, between 11pm and 6am tomorrow.
5:02pm: Police confirm the Southern Motorway is now open following a crash which earlier closed two southbound lanes.
The road is now open, however motorists are advised to take care as there is still a backlog of traffic in the area.
5:01pm: Traffic is easing slightly, but remains heavy on the southbound Southern Motorway.
Traffic between Fanshawe St offramp and Hobson St onramp is travelling at 7km/h.
Between the Port onramp and Khyber pass, traffic is travelling at 30km/h.
Between the Market Rd offramp and Greenlane Rd offramp, it is travelling at 15km/h, while between the Ellerslie Panmure Highway onramp and the South Eastern Highway offramp, it is travelling at 25km/h.
4.50pm: All lanes on the Southern Motorway Southbound are now open, but congestion remains heavy on and around the motorway and drivers should continue to avoid the area.
Auckland Transport says the crash has caused delays to Great South Rd and Howick & Eastern bus services of up to 30 minutes. People heading south are advised to consider delaying their trip or taking the train.
4:27pm: Police advise motorists who use the Southern Motorway to plan alternate routes home if possible.
Work is continuing to clear the road, with engineers at the scene.
Two southbound lanes remain closed.
The St Marks, Ellerslie and Greenlane offramps southbound are closed in an effort to minimise the amount of traffic heading into the area.
The New Zealand Transport Agency says the Southern Motorway southbound between Ellerslie and the South Eastern Arterial will be closed tonight for emergency structural repairs, due to a digger hitting Penrose bridge.
To minimise disruption to motorists the closures will be timed between 11pm and 5am, when traffic is lighter.
A signposted detour will be in place and drivers are asked to follow the signposted routes while work is being carried out to ensure that this section of the motorway is safe.
4:20pm: The Auckland Transport website shows traffic is backed up from the Fanshawe Street in the city to the Princess St offramp in Takanini. The black line indicates places where congestion is at its worst.
Traffic between Fanshawe and Hobson Sts is travelling at 7km/h. Between the Tecoma St offramp and onramp, traffic is travelling at 2km/h, according to AT.
4.12pm: Auckland Transport has advised that bus 550x travelling out of the city will use Great South Rd, rather than the motorway.
4.10pm: NZTA says traffic is still congested from the city to Penrose. Alternative route SH20 (South Western Motorway) is flowing well at present.
4pm: The Penrose bridge has been deemed safe for all vehicles. An NZTA spokeswoman said there are signs ahead of the bridge, warning motorists with overheight vehicles to pull over.
3.50pm: The current travel time between Hobson St in the city and Manukau is an hour and 12 minutes. The normal time is 15 minutes, according to Auckland Transport.
3.35pm: A man who was driving behind the truck carrying a digger that smashed into an overbridge on the Southern Motorway has described the moment he slammed on his brakes in anticipation of the accident.
The motorist, who wanted to remain anonymous, said he was in the right lane, heading south, behind the truck which was in the centre lane.
About 100 metres before the bridge, a flashing light went off, warning that the vehicle was too high.
In anticipation, the man slammed on his brakes. He said traffic was travelling at 100km/h at the time.
The arm of the digger smashed into the bridge, and the machine fell into the right lane in front of the man.
He estimated it had overlapped by just 20 centimetres.
The man jumped out of his vehicle and ran to the truck, pulling the driver out uninjured, but in shock.
3.20pm: Two Southbound lanes in Penrose are still blocked on the Southern Motorway, Southbound. On-ramps at Ellerslie-Panmure, Greenlane and St Marks Rd are now closed.
3.18pm: Southbound traffic between the city and Ellerslie is travelling at approximately 15 kilometres an hour, according to the NZTA.
3:15pm: Traffic heading south is at a standstill on the Southern Motorway from the city, after a truck carrying a digger in a trailer hit the Penrose overbridge.
The New Zealand Transport Agency says motorists should avoid the area, or expect long delays.
The agency recommends motorists use Great South Rd or the South Western Motorway as an alternative route.
Northbound traffic is also heavy on the motorway, from Highbrook.
The accident, at 1.15pm, occurred when the arm of the digger has hit the over bridge, part of the Ellerslie Panmure southbound onramp.
The onramp is being assessed for damaged and is currently closed.
There are no reported injuries and no other vehicles were involved, police said.
Emergency Services are on the scene.