Multiple vehicles have been caught up in a crash on Auckland's Northwestern Motorway - the second major incident to cause traffic delays on the network this morning.

Emergency services are responding to the crash just after the Rosebank Rd off-ramp, heading towards the city centre.

"A multi-vehicle crash has blocked multiple northbound lanes on SH16 just after the Rosebank Rd off-ramp," Waka Kotahi NZTA Auckland said.

"Pass the scene with care and be prepared for delays."

Motorists were also urged to keep "eyes on the road".

A traffic camera shows at least two fire appliances at the scene.

The incident comes after authorities confirmed all lanes on the Northwestern Motorway near Massey, West Auckland, had been reopened after a police incident earlier today shut down part of the motorway heading towards Westgate.

Police were called to an incident near Royal Rd, in Massey, about 6am and which forced the partial closure of the Northwestern motorway, causing a huge backlog in both directions.

Long delays are predicted. Photo / Waka Kotahi

By 7.20am, road authorities confirmed all lanes had since been reopened. However, motorists are still being told to expect delays as congestion eases.

Police have confirmed the situation has been resolved, but did not give details about the nature of the incident.

Motorists are being warned of long delays early this morning after an incident shut down part of Auckland's Northwestern motorway. Photo / NZ Herald

7.10am update

Authorities say one lane heading towards the city, coming from Westgate, has since been opened. However, all lanes heading towards Westgate remain closed as of just after 7am.

One motorist heading to work in the city said she had been stuck on the Westgate turn-off trying to get on to the motorway for about 45 minutes.

"Traffic is absolutely crawling."

Diversions are in place but Waka Kotahi NZ Transport Agency advises that northbound lanes are closed between Massey and Westgate.

Commuters are warned to avoid the area or face long delays, with delays predicted in both directions.

A police incident is causing heavy congestion on Auckland's Northwestern motorway this morning. Image / Google

Real-time traffic maps on Google show heavy congestion in both directions and motorists heading out this morning are encouraged to delay travel time or seek alternative routes.