Truck carrying gravel rolls on main route to Auckland Airport

The crash happened in the southbound lanes on State Highway 20. Photo / Keith Barrett

A truck carrying a large amount of gravel has rolled on one of the main routes to Auckland Airport.

The crash happened in the southbound lanes on State Highway 20, the Southwestern Motorway, near the Portage Road overbridge about 4.20pm.

Gravel covered the road.

The overturned truck. Photo / Chloe van Diepenbrugge

Motorists were asked to avoid the area, or use State Highway 1 as an alternative route.

Emergency services are at the scene and traffic management contractors worked to clear the road and get traffic moving again, police said.

Truck #crash on #SH20A (George Bolt Mem Dr) has both airport-bound lanes blocked. Please use #SH20B (Puhinui Rd) as alternate ^TP pic.twitter.com/xV8y8AeVtF

— Waka Kotahi NZTA Auckland & Northland (@WakaKotahiAkNth) December 20, 2016

NZTA tweeted that the southbound lanes were now clear, though congestion remained.

UPDATE: Southbound lanes on Southwestern Mwy between Massey Rd & Puhinui Rd NOW CLEAR. Congestion remains from Mangere Bridge ^TP

— Waka Kotahi NZTA Auckland & Northland (@WakaKotahiAkNth) December 20, 2016

UPDATE: Truck #crash on #SH20A (George Bolt Mem Dr) NOW CLEAR from airport-bound lanes. Congestion heavy in area, but easing ^TP

— Waka Kotahi NZTA Auckland & Northland (@WakaKotahiAkNth) December 20, 2016

#SH20A UPDATE: Congestion has eased. Now taking 23 mins Gillies Ave (via Route12) to @AKL_Airport. Check here: https://t.co/7OLZsNUGn5 ^TP pic.twitter.com/YLNhn44H6B

— Waka Kotahi NZTA Auckland & Northland (@WakaKotahiAkNth) December 20, 2016

Auckland Airport tweeted "traffic is now flowing through all airport roads and congestion has eased".

Traffic update - traffic is now flowing through all airport roads and congestion has eased.

— Auckland Airport (@AKL_Airport) December 20, 2016