The 7.3-magnitude earthquake struck off the main island on Tuesday, toppling concrete buildings in Port Vila and setting off landslides.

It has damaged water supplies, knocked out mobile networks, halted operations at the capital's main shipping port and led to a suspension of commercial flights.

Ten people have been confirmed killed so far, according to ministry of health figures relayed Thursday by the United Nations' humanitarian affairs office.

Two of the dead were Chinese and one French, their embassies have confirmed.

Toll figures issued by the authorities have sometimes been contradictory as officials grapple with the disaster.

Vanuatu President Nikenike Vurobaravu said there were "around 16 dead", citing the police, in a televised address posted by the public broadcaster VBTC News to social media.

About 80,000 people have been directly affected by the earthquake in the archipelago of 320,000, which sits in the Pacific's quake-prone Ring of Fire, the UN said.

More than 14,000 of them are children.

Australia and New Zealand have dispatched more than 100 personnel, along with rescue gear, dogs and aid supplies, to help hunt for survivors and make emergency repairs.

There are "several major collapse sites where buildings are fully pancaked", Australia's 69-strong rescue team leader Douglas May said in a video update provided by Canberra on Friday.

- Pile of concrete -

"Outside of that, there's a lot of smaller collapses around the place," May said.

"We're now starting to spread out to see whether there's further people trapped and further damage. And we've found numerous places of collapse east and west out of the city."

In Port Vila, rescuers have focused on two disaster areas: a four-storey building housing a supermarket, hotel and garage in the north in which the ground floor was flattened, and a two-floor shopping block in the city centre that crumbled into a flat pile of concrete.

The shopping block is where "most of the lives have been lost", Vanuatu's Emergency Services Association acting manager Jeff Mabbett told AFP.

His rescue team was on-site minutes after the quake hit, rescuing those they could.

Four days on, the unit was still digging through landslides and the rubble of buildings.

The rescue effort was being hampered by "limited access to heavy machinery, very small spaces, poor lighting and multiple large aftershocks", Mabbett said.

- Tourist medics help out -

A second team was providing medical support, including setting up a field hospital for survivors.

"We have seen over 100 patients in the three days post-earthquake, with a range of ailments," Mabbett said.

"We are lucky to have had the kind support from tourists who are paramedics, doctors and nurses from Australia and New Zealand who have assisted us with clinical staffing until their repatriation flights took off."

Rescuers were tired but in "good spirits", he said.

The quake also wrecked a building housing the US, French, British, Australian and New Zealand diplomatic missions. The ground floor along half of that four-storey structure was flattened, but no deaths were reported.

The government has declared a seven-day state of emergency and a night-time curfew.

"One concern now is that there are reports of 900 people displaced out of their houses and who have been sleeping outside for the last few days and nights, without proper access to water and sanitation facilities," said Philippe Guyant, a World Health Organization medical officer in Vanuatu.

Vanuatu has usually been able to set up refuge for disasters such as cyclones, he told AFP.

"But this time there was no evacuation centre, and people have stayed out for so long. There is a mix of people, some fearing to go back to ... their houses destroyed in the earthquake."