A state of emergency has been declared in Vanuatu after a powerful earthquake hit the Pacific island, damaging many buildings in the capital Port Vila and killing at least six people and injuring dozens.

Witnesses told Agence France-Presse that bodies could be seen lying in Port Vila after the 7.3 magnitude quake, which struck on Tuesday at a depth of 57km (35 miles), 30km off the coast of Efate, Vanuatu’s main island, at 12.47pm (0147 GMT), according to the US Geological Survey.

State broadcaster VBTC showed footage of vehicles crushed under the debris of collapsed buildings and boulders strewn across a highway. Drone footage showed landslips near a shipping terminal.

An official at Port Vila’s hospital told VBTC that six people had died and more than 50 were injured.

On Tuesday evening, the caretaker prime minister, Charlot Salwai, declared a state of emergency and said a curfew would be imposed for seven days in the worst affected areas.

It was a “sad and devastating time” in Port Vila, he said, expressing sympathy to families who had lost loved ones.

The United Nations office for the coordination of humanitarian affairs estimated 116,000 people had been affected by the earthquake. It said there were six unconfirmed deaths and damage to the two main water reservoirs.

The structure of the hospital in Port Vila was affected, with the operating theatre not functioning and triage tents set up outside to manage the influx of patients, it said in a statement.

Australia was among the first countries to respond to Salwai’s appeal for assistance from the international community.

Penny Wong, Australia’s foreign minister, said her government was preparing to deploy immediate assistance on Wednesday, including urban search and rescue and emergency medical teams.

Information about the extent of the damage has been hampered by disrupted communications, with phone lines and government websites down, but reports of widespread destruction began to emerge on social media in the hours after the quake.

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“There’s people in the buildings in town. There were bodies there when we walked past,” Michael Thompson, a resident, told AFP by satellite phone after posting images of the destruction on social media. A landslide on one road had covered a bus, he said, “so there’s obviously some deaths there”.

As well as destroying the ground floor of the diplomatic building, the quake also knocked down two bridges and toppled other buildings, Thompson said.

The bottom floor of the embassy block “no longer exists,” he said. “It is just completely flat. The top three floors are still holding but they have dropped.

“If there was anyone in there at the time, then they’re gone,” said Thompson, who runs a zip wire adventure business in Vanuatu.

The French ambassador to Vanuatu and Solomon Islands, Jean-Baptiste Jeangene Vilmer, posted on social media: “Many victims in the country, flights suspended, communications cut, no water or electricity, we are organising relief.”

A Red Cross spokesperson in Fiji said workers on the ground were reporting significant damage. Footage shared by the Vanuatu Broadcasting and Television Corporation showed crowds outside the Vila central hospital appearing to lift injured people on to stretchers.

Dan McGarry, a journalist based in Port Vila, told the Associated Press he saw three people on stretchers “in obvious distress”, outside the hospital. “It was the most violent earthquake I’ve experienced in my 21 years living in Vanuatu and in the Pacific Islands,” McGarry said. “I’ve seen a lot of large earthquakes, never one like this.”

Many large buildings have collapsed in Port Vila, electricity is out and water has been cut in most of the capital, Care Australia, a non-profit humanitarian agency, said in a statement. One video posted on social media appeared to show crumpled buildings in Port Vila, including one that had collapsed on to cars.

A building housing a number of diplomatic missions in Port Vila – including those of the US, Britain, France and New Zealand – was significantly damaged, New Zealand’s foreign ministry said. Officials were in the process of accounting for New Zealand High Commission staff, a spokesperson said.

Wong said all Australia’s embassy staff were safe, while the US embassy said all its staff were also safe.

A video posted to social media depicted the building with some damage to its structure, including buckled windows and debris that had crumbled from walls to the ground. Other photos and videos showed items and shelves that had tumbled to the floors of shops and landslides that appeared to block roads.

A 5.5-magnitude aftershock struck minutes after the main quake, followed by a string of lesser tremors over the following hours.

The US tsunami warning system cancelled an initial tsunami warning for the island nation, which is made up of 80 islands and home to 330,000 people.

Videos shared on social media also showed an image of a landslide triggered by the quake.

The Australian prime minister, Anthony Albanese, said in a statement on X: “Australians are thinking of our friends and neighbours in Vanuatu after the devastating earthquake that struck their home this afternoon. We are closely monitoring the situation and stand ready to assist the people of Vanuatu in any way we can.”

Australian and regional airlines cancelled or diverted flights.

Earthquakes are common in Vanuatu, a low-lying archipelago that straddles the seismic Ring of Fire, an arc of intense tectonic activity that stretches through southeast Asia and across the Pacific basin.

“In this region, where the tectonic plates converge is one the world’s most seismically active plate boundaries,” said Prof Meghan Miller, from the research school of earth sciences at the Australian National University. “The earthquake hypocentre was fairly deep, about 57km, which means there was no tsunami generated. However … the island experienced very strong shaking, likely resulting in moderate damage to structures.”

New Zealand’s foreign ministry said 37 New Zealanders were registered as being in Vanuatu, but did not provide any further details about their status.