UPDATED 9.23PM Police have confirmed passengers involved in a serious bus crash near Akaroa this evening were tourists on a day outing from a cruise ship anchored in Akaroa Harbour.

Two people are in a critical condition and five are seriously injured after a bus and a car collided, sending the bus careering down a bank.

Senior Sergeant Vaughn Lapslie, of Christchurch, said police were told there were 32 people on the bus and they were from the ship.

Police did not have the nationalities of those involved, Lapslie said.

The vehicles collided just after 5pm and the bus ended up in the foliage off the side of the road near the intersection of Summit Rd and the Christchurch-Akaroa Rd, police said.

"While the investigations are ongoing, police will not speculate on the cause of the collision," Lapslie said.

LISTEN ABOVE: Newstalk ZB reporter Sam Olley spoke with Larry Williams earlier this evening

St John Ambulance Controller Sean Lester said the pair with critical injuries, and one person with serious injuries, had been rushed to Christchurch Hospital by helicopter.

Four others seriously hurt as well as one person with moderate injuries were taken via ambulance.

The remaining 26 occupants of the vehicles involved - who either had minor or no injuries - were taken to Akaroa Fire Station where paramedics treated them.

The bus passengers left about 8.30pm to return to the ship.

Earlier, firefighters had to cut one person from the car and the bus driver out of the wreckage, a Fire Service spokeswoman said.

Three fire engines, at least four ambulances and at least one police car were at the scene.

A staff member at the Hilltop Tavern, near the crash site, told the Herald he took water to the victims.

Camera operator Matthew Simons said he could see the bus about 50m down the bank and a blue wagon-like Toyota on the road.

Simons believed he'd seen one of the bus passengers emerging but couldn't be sure.

There was "a whole heap of firefighters working around the bus".

Firefighters had to use the jaws of life to cut the roof off the small, light blue ​car.

Debris from the smash was strewn on the road and the front of the car was mangled.

Pieces of the car were lined up on the side of the road, resting on a bank.

​Photos from the scene also showed the wreckage of the bus lying on its side among the foliage.

People could be seen scrambling to get to the bus to help.​

A crowd gathered at the police cordon around the next bend in the road.

Three white buses and several cars were pulled over.

A worker at the Hilltop Tavern told Newshub the crash happened just around the corner from the bar but he couldn't see the scene from where he was.

A customer told him multiple people were injured.

He said the hill was steep and if a bus went down there, it would be of concern.​​

The Christchurch-Akaroa Rd is now closed between Summit Rd and Barry's Bay Rd.

Police have set up cordons and officers are directing motorists on to Pigeon Bay Rd, which links up to Summit Rd.

The diversions set up following the crash are expected to be lifted later tonight.

The Commercial Vehicle Investigation Unit and the Serious Crash Unit will investigate the incident, and a scene guard will remain at the site overnight, police said.

Fairfax reported that the tourists on board the bus were cruise ship passengers, believed to have been visiting New Zealand on the Celebrity Solstice vessel.

The ship has capacity for 2850 passengers and 1250 crew members. It was expected to dock at Akaroa Harbour today.

Tragedy has struck Celebrity Solstice on New Zealand roads three times in the last few months.

A Canadian passenger from the ship was severely injured when he was hit by a campervan while cycling with his partner on Otago Peninsula last week. He has since recovered.​

An elderly American woman who was on board a November sailing was killed while riding a bike in Tauranga the day the ship arrived in the city. The 71-year-old was struck by a truck near the harbour bridge.

The same afternoon a bus carrying passengers from the same ship collided with a car on State Highway 29. The car's driver died after the crash. No one on the bus was injured.