Motorists travelling from Manukau to Auckland city should allow up to an hour on the motorway this morning as a spilt load and accidents leave traffic moving along at a snail's pace.

New Zealand Transport Authority Auckland spokeswoman Sarah Azam says the knock-on effect from an earlier incident where a truck lost its load of plastic lunch boxes and drink bottles has resulted in the usual trip taking much longer than usual.

This has been compounded by a "myriad of issues" including accidents, breakdowns, school traffic and people returning to work after the holiday weekend.

Ms Azam says while the travel time along the Southern Motorway has improved from the 80-plus minutes it is still a lengthy trip.

"It's starting to pick up now but you'll still need to allow plenty of time for your journey," she says.

The latest incident adding to this morning's headache commute was a multi-car crash near Papakura.

The traffic agency warned people to exercise patience.

"Multi-car #crash on Sthn Mwy prior to Papakura will cause further delays for citybound motorists. Both lanes open. Pls #BePatient "

Ms Azam says the knock-on effect from the first incident, which happened before 6am this morning, is still being felt hours later.

"There has been a myriad of issues. It kicked off with someone losing a load of plastic bottles and lunch boxes followed by quite a few accidents and breakdowns which have all converged to make it very slow going this morning," she says.

The unsecured load which triggered today's disruption was spread across three lanes and stretched 150m along the motorway.

Road sweepers were needed to clear the debris.

Ms Azam says traffic is starting to pick up now but people still need to allow up to an hour to make the trip along the Southern Motorway into the city.