Two investigations are under way into the death of a 26-year-old man in a car crash after a police chase in central Christchurch early today.

The man was killed and five others injured when a Mitsubishi Lancer crashed into a power pole at the intersection of Manchester St and Moorhouse Avenue around 1am.

Police said that a patrol car stopped the vehicle for a routine check on Manchester Street but the car sped away as officers approached it.

Police gave chase for a few streets before finding the vehicle smashed into the concrete pole.

Inspector Al Stewart said the 26-year-old man, a front seat passenger, was killed in the impact, the driver and another passenger were critically injured, and another passenger seriously injured. The two remaining passengers received minor injuries.

All the injured were taken to Christchurch Hospital.

Mr Stewart said the Mitsubishi at one point ran a red light during the pursuit.

The death is the ninth associated with police chases in less than a year. Police have yet to release the victim's identity.

Three weeks ago, a 22-year-old man was killed in Christchurch when his car hit a tree as he was trying to get away from police.

Each incident came down to individuals choosing to drive dangerously and place passengers at risk, Mr Stewart said.

Mr Stewart said two investigations were underway into the latest fatal crash - by police and the Independent Conduct Authority (IPCA)

The fatal crash was not believed to be connected to the arrest of 30 people after a boyracer gathering in the north of the city at about 1.30am.

Police reported 140 drivers blocked the northern motorway at Chaney's, north of Christchurch, at about 1.30am today.

"The group of about 140 blocked the onramp with their vehicles and created a danger to other road users due to their driving behaviour and general disorderly presence," Mr Stewart said.

Boyracers had been given every chance to moderate their behaviour, through fines and vehicle seizures, but still had not got the message, he said.

He said those arrested faced charges ranging from unlawful assembly to disorderly conduct - punishable by up to a year in prison.

The incident comes just days after Christchurch City Council implemented a bylaw targeted at boyracers under which drivers caught repeatedly "cruising" the city's main streets can be fined up to $1000.

The council is the first in New Zealand to exercise new powers under a law change last year that enabled local bodies to control, restrict or ban cruising.