Six people, including a baby, were injured today after a speeding car pursued by police ploughed across a concrete median and into oncoming traffic on a busy Christchurch street.

Three major police investigations have been launched into the accident which happened just before 10am, on Buckleys Rd, outside Eastgate Mall in Linwood.

Police said they were not chasing the white Pontiac, but were following it after officers had stopped it nearby, only for the car to speed away.

Two of the three men in the pursued car are thought to have suffered the worst injuries, with one in intensive care and the other described tonight as seriously ill.

Canterbury District Health Board spokeswoman Vivienne Allan said another man was taken to the emergency department. It was not clear tonight if he had been admitted.

She said a 12-month-old baby and its parents, who were in a green Subaru struck by the Pontiac, were also admitted. Their conditions were not thought to be life-threatening.

It is understood the Pontiac was first stopped by two police officers on the corner of Gloucester St and England St.

The Pontiac allegedly did three "donuts" before leaving one officer standing there while the other pursued the car.

It swiped another car on Pages Rd before turning into Buckleys Rd.

Police estimate the car was travelling at 100km/h before it crossed the raised median strip, crashed through a lamppost, clipped a small tree, then rammed the Subaru, which was also hit by a campervan following behind. The campervan occupants were not seriously hurt.

Inspector Gary Knowles, of Christchurch police, said criminal, serious crash unit and Police Complaints Authority investigations had all been launched.

"We weren't chasing the car. The vehicle was stopped by police earlier and it took off.

"It was not a close pursuit. My understanding from initial witnesses is the police car was some distance from it," Mr Knowles said.

Police appeared to have acted according to "protocols", but communications tapes were being analysed to check everything was done properly.

Mr Knowles said that police knew the men in the car.

Witness Peter Shearman said the crash would have happened even if the police had pulled out earlier.

"... these guys were going for it. Nobody touched him, he just lost it," Mr Shearman said.

Andrew Pritchard, who also just avoided the smash, said he was surprised the accident was not worse.