A navy ship was steaming towards the seaside town of Kaikoura, which bore the brunt of the quake that claimed two lives when it struck early yesterday.
Huge landslides have cut road and rail links to the town, where police say water is running low, power is intermittent and hundreds of people are staying in evacuation shelters.
It has a population of 2,000, which Prime Minister John Key said was bolstered by an extra 1,200 tourists attracted by the area's popular whale-watching cruises.
He said four military helicopters would begin ferrying the trapped visitors, mostly international backpackers, in small groups to Christchurch from early today.
Naval ship HMNZS Canterbury would take hundreds more when it arrives, likely tomorrow, he added.
"It's more water and food, it's more chemical toilets, it's fixing up the road access, getting those tourists out and then ultimately the big clean-up job," he told TVNZ.
The Defence Force said a C-103 Hercules was also on standby to drop supplies, while state broadcaster Radio New Zealand reported up to 50 civilian helicopters could also be drafted into the tourist evacuation effort.
The Canterbury set off from Auckland late yesterday and its commanding officer Simon Rooke said the ship could take up to 500 tourists.
Heavy rain and driving winds were hampering clean-up efforts, although life outside the main Kaikoura disaster zone was slowly returning to normal.
There have also been more than 800 aftershocks, some measuring more than 6.0, further complicating the work of emergency crews.
The tremor, one of the most powerful ever in the quake-prone South Pacific nation, hit just after midnight yesterday morning.
It triggered landslides that dumped mountains of rocky debris on a main highway and ripped railway tracks 10 metres (30 feet) off course.
One person was believed to have died at a historic homestead that collapsed at Kaikoura, with another killed at a remote property north of Christchurch.
It was felt across most of the country, causing severe shaking in the capital Wellington, about 250 kilometres (155 miles) away.
It also set off a tsunami alert, with sirens sounding and police and emergency workers going door to door to evacuate seaside properties.
While officials initially feared waves of up to five metres (16 feet), they only reached about two metres before the alert was lifted.
Key flew over the quake's epicentre yesterday and said he was shocked to see such "utter devastation".
Key said New Zealand's strict construction codes meant its buildings were high quality and tourists' chances of being caught in a tremor were "truthfully very low".