At least three pedestrians are injured after a bus smashed into a store in the Auckland suburb of Birkenhead today.

A witness said the AT bus, with passengers on board, had crashed into a computer shop on Birkenhead Ave, next door to the Tongue and Groove Cafe.

"It came across the side of the road, through a barrier and into the building. I am in shock. It is massive."

Allstar apprentice plumber Isaac, who was travelling in his van the opposite direction to the bus, said he had stopped for two adults and two kids aged under 10 at the pedestrian crossing.

"I saw the whole thing. [The bus] pulled straight from the bus stop [through the crossing]. I'm not sure if they hit the accelerator instead of the brake," Isaac said.

"It came out of nowhere. I was lucky not to get hit. If I had been 2 metres ahead I would've been hit directly on the driver's side."

There were quite a few passengers on the bus, he said.

"They all got out of the bus real quick."

After the bus hit the shop he saw one of the people on the pedestrian crossing - a woman - crying.

A child lying on the ground was screaming, and was picked up and being comforted.

"They didn't want to move the fella, the man."

The man was aged about 40 and was conscious and talking, Isaac said.

Nicsons pet shop owner Susan Hung said three people - a man and two children - were injured, with the man still being attended to on the crossing.

"There was a loud noise, and then lots of screaming... and people were running into the cafes and shops. We gave them some of the pet blankets to keep the man warm."

The man was being treated in the middle of the road, with blankets covering him.

He was conscious, with his eyes open.

"The children are screaming and crying and they are being taken to the ambulance."

A woman who was with the trio was not injured.

"I have heard from people who are saying the driver may have pushed the accelerator rather than the brake... I'm not really sure. My husband said the bus was going very fast," Hung said.

The bus had swerved to the right, crossing the centre line and smashing into the glass front of the computer store.

"I'm just shocked.. All we had was pet blankets to keep him warm," said Hung, as sirens wailed in the background.

She did not see anyone on the bus and did not know if any passengers or the driver had been injured.

The bus had clipped an Allstar Plumbing van, stopped at the crossing, before crashing into the building.

An Allstar Plumbing spokesman said he had spoken to the van driver, who was not injured

The owner of The Gelato Workshop said the bus had crashed into the Free 4U Computing building, about 10m away from his shop.

He said it looked like a man had been crossing the road, and the bus had swerved to try to avoid him.

The three pedestrians had minor injuries, and were being treated at the scene by St John Ambulance.

A police spokesman said he was unable to confirm the exact nature of the injuries at this stage.

"There are no reports of anyone on the bus or inside the building receiving injuries," he said.

Cordons are currently in place on Birkenhead Ave at the intersections of Onewa Rd and Mokoia Rd.

Motorists are advised to avoid the area.

A Fire and Emergency spokesman said it appeared the bus had hit three pedestrians and then crashed into a shop in Birkenhead Ave, near Hammond Pl.

Auckland Transport spokesman Mark Hannan confirmed three people were injured.

Their injuries were not thought to be serious.

He said AT had a staff member at the scene and a full investigation into the incident had started.