THE New Zealand city of Christchurch has been hit by an earthquake - four months after 181 people were killed by a 6.3-magnitude shock, it was reported.

A magnitude 5.5 tremor rattled the quake-prone city, twinned with Christchurch, Dorset, at 1pm local time today sending people fleeing from buildings, and boulders tumbling down hillsides.

Police said there were no initial reports of injuries.

The quake was located six miles south-east of the central city at a depth of 6.8 miles.

Aftershocks sent boulders on the city's Port Hills tumbling towards housing, while parts of the eastern city were flooded, it was reported.

Christchurch has experienced a number of strong earthquakes since a magnitude 7.1 quake struck the city on September 4 last year.