Two southbound lanes on the Southern Motorway at Penrose were blocked after a vehicle hit the overbridge.
But the New Zealand Transport Agency (NZTA) says three lanes South-bound on the Southern Motorway are now open, however congestion remains heavy on and around the motorway
A digger on the back of a trailer hit the Penrose overbridge around 1:15pm. Engineers are currently on the scene working to clear it. Motorists can monitor NZTA on Twitter for updates.
Traffic in the northbound lane has slowed due to rubberneckers, NZTA acknowledged in a tweet.
"Although the motorway is currently open, the accident is causing congestion and motorists are advised to avoid the area to prevent delays to their journey," police said in a statement.
NZTA recommends motorists use the Southwestern Motorway instead.
The accident follows a breakdown which blocked traffic heading towards the city on the Southern Motorway this morning, near Lambie Dr.
A rolled truck caused delays on the Northwestern Motorway this morning too.
The Penrose Road bridge is frequently hit by vehicles too tall to fit underneath it. In October 2015 it was struck by a motorhome, the driver fleeing before authorities arrived.
In 2012 a truck carrying sheets of glass smashed into it, with onlookers saying the panes exploded into a white cloud.
The most recent incident was in March when a truck and trailer unit hit it, blocking traffic all the way back into the city at Fanshawe St.