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 Monday.
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, bolstered by an extra 600-1,000 tourists attracted by the area's popular whale-watching cruises.
Officials said they were ramping up efforts to rescue the visitors, who are mostly international backpackers.
Four military helicopters will begin ferrying them in small groups to Christchurch on Tuesday and a C-103 Hercules is on standby to drop supplies to the stricken town.
State broadcaster Radio New Zealand reported up to 50 civilian helicopters would also be drafted into the rescue effort, evacuating tourists from local rugby grounds
The HMNZS Canterbury set off from Auckland late Monday and is expected to arrive in Kaikoura early Wednesday
Commanding officer Simon Rooke said it could take up to 500 tourists
"We're going to pick them up by landing craft and sea boats and extract them to Lyttelton (in Christchurch) so they can get to a point of safety," he said
Heavy rain and driving winds were hampering clean-up efforts, although life outside the main Kaikoura disaster zone was slowly returning to normal as roads opened and power was restored
There have also been more than 800 aftershocks, some measuring more than 6.0, further complicating the work of emergency crews.
