One person has been taken to hospital after a school bus carrying dozens of students crashed through a motorway overbridge fence, leaving the front of the vehicle dangling in mid-air.

A total of 24 people were assessed for injuries after the single-vehicle crash in Auckland's Newton Rd just after 8am today.

The crash has caused extensive traffic delays through Khyber Pass Rd and in Ponsonby.

A St John spokeswoman confirmed one person was taken to Auckland City Hospital with minor injuries. A total of 24 people were assessed at the scene and some had minor injuries.

St John received the first call to the incident at 8.04am. An ambulance and a rapid response vehicle were sent to the scene.

The Coachways NZ bus crashed through iron gates and came to a rest wedged on the footpath on the bridge, which is above the Northwestern Motorway.

A staff member at the company referred inquiries to their boss, who was unavailable as he was at the crash scene.

Photo / Akula Sharma

Photos and footage show the front half of the bus hanging over the bridge.

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The high school students on the bus were transferred to a nearby bus after being checked by St John ambulance staff.

Both directions of the overbridge were closed, as vehicle recovery takes place.

Firefighters work to cut through the fence. Photo / Cheree Kinnear

Firefighters had to cut apart parts of the fence and are now hooking the bus up to pull it out.

An inflation device was placed under the vehicle to raise it up and then winch it to safety.

The crash has caused extensive traffic delays in the area, with vehicles backed up down Khyber Pass Rd and Ponsonby Rd on the other side of the bridge.

'It looked precarious'

Waitematā local board member Glenda Fryer was heading to Newmarket to hand out election leaflets when she came across the crash.

She believes she arrived about a minute after the incident happened, as the children on the bus were starting to get off the bus and emergency services had not arrived yet.

"The kids on the bus were filing out. There wasn't anyone weeping or panicking.

"I was very worried that someone had been injured, [but] there was no one crying or screaming.

"But it looked rather precarious, especially if you were at the front of the bus."

Several fire engines and police vehicles are at the scene.

Auckland Transport is asking motorists to follow the direction of emergency services.

Bus commuters are being advised to check their bus schedules this morning as a result of the crash.

There are delays to several services in the area.

Auckland Transport is telling people: "Allow extra travel time."