Five people have been killed in a horrific single-car road crash in Timaru, and police say speed is believed to have been a factor.

The car was overloaded, and there were insufficient seats and restraints for the number of people travelling.

"To have five lives lost in an instant is a terrible tragedy, and our thoughts are with their families," Superintendent Steve Greally, of the National Road Policing Centre, said.

He said not everybody in the car was wearing seatbelts.

"This is incredibly frustrating," Greally added. "Particularly in a small community, the impact of a crash like this stretches far, and everyone in the area will be hurting."

Police confirmed multiple deaths in the crash, at the intersection of Seadown Rd and Meadows Rd in Washdyke, at about 7.20pm on Saturday.

"This will be extremely devastating," Timaru mayor Nigel Bowen said.

"It is devastating for the district, and from what I hear, a lot of kids were pretty frantic last night trying to find out if their friends were involved.

"It's pretty saddening for the community, and something that hasn't happened in our township for a long time."

Five people were killed and another person was extricated from the wreck and taken to hospital.

Police this morning said a sixth person, the driver of the car, was taken to Timaru Hospital last night in a serious condition.

Aoraki Area Commander Inspector Dave Gaskin said: "Sadly, a number of people died at the scene.

"The road will be closed for a significant period of time while a scene examination is undertaken."

Police confirmed it was a single-vehicle crash after it had earlier been reported as a two-car crash.

One person was hospitalised after the crash but police did not initially confirm the total number of people in the car.

Fire and Emergency shift manager Andrew Norris said 13 staff attended the crash scene.

"We responded with units from Washdyke, a fire engine from Timaru and a second rescue tender from Temuka to the north," Norris said.

"They extricated one person from the scene and assisted with the other agencies. But there was only one extrication that was performed at the scene that I'm aware of."

Norris said the Serious Crash Unit was working at the scene and Fenz might be required to go back later.

"Not the sort of thing crews want to be faced with."

The road is closed and motorists were asked to avoid the area.

Police said more information would be released when available.