Wellington, Sept 5 NZPA - KiwiRail is sending almost 300,000 litres of water to Christchurch.

KiwiRail chief executive Jim Quinn said the water would arrive aboard a train early this afternoon and was in response to the city's need for fresh water as a result of earthquake damage following yesterday's 7.1 magnitude quake.

About 15 percent of the city remains without water, and those with it are being urged to use it sparingly. Any drinking water should be boiled for at least three minutes.

"It's a practical contribution we can make to Christchurch's emergency response and we will be looking for other ways that rail can be used to support the region's recovery," he said.

"We are grateful to Fonterra for making the tanks available for the shipment."

KiwiRail opened the railway line south of Christchurch last night but continuing aftershocks meant a speed limit of 40kmh had been imposed. That was reduced to 25kmh over bridges.

"We still have work to do repairing damage to the track and one bridge between Belfast and Rangiora. We will be road bridging freight to Christchurch from Rangiora while this work is being completed," Mr Quinn said.