A large tree and slip has forced the closure of a major Auckland highway this morning.

The New Zealand Transport Agency (NZTA) warned motorists to expect delays on State Highway 20 after the tree came down between the Neilson St off-ramp and Hillsborough Rd on-ramp.

The northbound lanes are blocked and detours are in place.

A police spokesperson said several concerned motorists called them at around 1am with reports of the tree blocking the road.

“Police provided traffic management until road closures could be put in place,” the spokesperson said.

Further down the highway, a crash blocked the Neilson St off-ramp at 7.30am.

It is unclear whether that crash was related to the traffic management measures put in place after the slip.

The crash was cleared by 8am but northbound lanes on SH20 remain closed while the slip and tree are removed.

Auckland Transport has warned bus users there will be delays on routes 38 and 309.