A main Christchurch river has burst its banks after a night of heavy rain.

The Heathcote River has overflowed, and is causing flooding in nearby areas.

Newstalk ZB's Chris Lynch says the water is overflowing onto roads and lapping at people's driveways although it hasn't reached any houses yet.

He said traffic in Christchurch is eerily quiet, and the NZ Transport Agency is telling motorists to avoid driving in Christchurch this morning unless they have to.

Cyclone Cook is now off to the east coast of the South Island and heading south. Much of the South Island is now under severe weather watches.

Advertisement

The cyclone is weakening but heavy rain is expected to pelt parts of the South Island this morning.

The system was centred just east of Kaikoura at 5.30 this morning and is moving south.

MetService meteorologist John Crouch says bands of heavy rain have been affecting parts of Wellington, eastern Marlborough and Canterbury overnight.

He says those bands of rain will ease in Wellington fairly shortly this morning.

However, John Crouch says some bands of rain could continue to affect Canterbury and the Kaikoura coast through to mid to late morning.

He says localised falls could generate a bit of surface flooding in the Christchurch area.

South Island firefighters have gone to three Canterbury homes who have called for help with flooding as heavy rain drenches the region.

A Fire Service spokesman said this morning's flooding, which happened in Rangiora and Kaiapoi, was very minor and was only affecting land surrounding the homes.

"It's very quiet compared with what we were expecting," said the spokesman.