New Zealand Prime Minister John Key said Monday that the country is well placed in principle to withstand the costs of another major earthquake.

Aftershocks continued to plague Wellington and the top of the South Island after Sunday's 6.5 magnitude jolt which struck in the Cook Strait at 5.09 p.m.

More than 100 aftershocks have been recorded since, including a 5.0 one which hit 15km east of Seddon at 10:47 a.m. this morning.

GNS Science said there's a 20 percent chance of a tremor greater than 6 hitting the same region in the next week.

Prime Minister John Key has assured quake-hit Wellingtonians that the government would do its "very best" to ensure they get the support they need.

Key had a brief stand-up with media before visiting the Wellington Regional Emergency Management Office for an update on the earthquake damage from Civil Defence controller Bruce Pepperell.

Key also met Wellington Mayor Celia Wade-Brown and Greater Wellington Regional Council Chairwoman Fran Wild.

Wellington mayor Celia Wade-Brown said Monday the capital came through Sunday's magnitude 6.5 earthquake very well.

She said it appears most of the damage on Monday is concentrated in the central business district but infrastructure and buildings have been largely "unscathed", Radio New Zealand reported.

Wade-Brown said engineers are double checking infrastructure and people should stay away from the central city all day.

She said engineers are making visual inspections and have identified superficial rather than structural damage. It is up to building owners to get a more thorough assessment, she added.

Emergency management staff are going through the central city, street by street, to assess the safety of buildings after Sunday's magnitude 6.5 quake.

The Fire Service has set up a command unit on The Terrace to provide support to Urban Search and Rescue engineers and technicians.

New Zealand government geological agency GNS Science said the 6. 5 magnitude quake at 5.09 p.m. Sunday was centred off the Marlborough coast at a depth of 17 km. A second quake, registering magnitude 5.2, occurred minutes later.

Some of the continuing aftershocks were also strong.

There had been 109 quakes from 7.09 a.m. on Sunday to 5.30 a.m. on Monday.

Some shops in central Wellington are open again, but the city centre is much quieter than usual.

Civil Defence acting city controller Neville Brown told Radio New Zealand that parts of Willis, Bolton and Featherston Streets are still closed because of suspected damage to buildings.

Earlier, Civil Defence Sunday controller Bruce Pepperall said the Regional Council on Wakefield Street, City Council offices and the Town Hall remain off limits on Monday morning until further inspection.

Wellington Regional Council chair Fran Wilde said there was extensive flooding at her council's building and stairwells were also being checked for damage. The council was due to vacate the building later this year.

While there appears to be no major damage to transport networks, train services are suspended until all roads, bridges and tracks have been signed off by engineers.

There will be no bus replacement service. Ordinary bus services are expected to operate as usual.

Civil Defence said people should travel only if it is essential, and commuters in the greater Wellington region are advised to drive with patience and care.

All customers of Wellington Electricity Lines have been reconnected. About 3,500 houses in Kaori and Wainuiomata were without power immediately after the quake.

Wellington airport is open and operating, but the runways are being checked regularly after big aftershocks, which may see some minor delays.

Wellington hospital has not reported any damage, but four patients with minor injuries were treated after the quake. Endi