The Transport Agency says there will be major traffic delays in central Auckland this weekend if people don't listen to warnings to stay away during the closure of part of State Highway 1.
The southbound lanes of the Southern Motorway between Gillies Ave and Greenlane are being closed for up to 36 hours from 5pm on Saturday.
During that time, the Newmarket Viaduct will be joined to the Southern Motorway.
Up to 60,000 vehicles that usually use the road on a Sunday will have to be diverted.
The Transport Agency says the diversion routes aren't big enough to cope with the usual traffic volumes, so motorists are being advised to keep clear of Newmarket.
While the motorway is closed, passengers are able to travel on trains free of charge.