WELLINGTON, New Zealand — A powerful magnitude 7.3 earthquake struck just off the coast of Vanuatu on Tuesday, causing widespread destruction in the South Pacific island nation as the injured began arriving at a hospital and unconfirmed reports of casualties emerged.

A tsunami warning was called off less than two hours after the quake. With communications still down hours later and official information scarce, witness accounts of casualties began to surface on social media and through patchy phone calls.

The earthquake happened at just before 1 p.m. at a depth of 35 miles and was centered about 19 miles west of Port Vila, the largest city in Vanuatu — a group of 80 islands that is home to about 330,000 people. It was followed by a magnitude 5.5 aftershock near the same location, with tremors continuing throughout the afternoon and evening.

It was not immediately clear how much damage was caused as phone lines and government websites remained down. In the first official information published on social media, the Geohazards Department said its monitoring systems remained offline due to power outages.

Residents were urged to stay away from coastlines for at least 24 hours — and until tsunami and earthquake monitoring systems were operational once again. No confirmed reports of damage or casualties were provided, but accounts detailing widespread destruction filtered out on social media and in interviews.

Crowds outside the hospital

Dan McGarry, a journalist based in Port Vila, told The Associated Press he heard of one death from a police officer outside Vila Central Hospital. McGarry saw three people on gurneys “in obvious distress,” he said.

Doctors were working “as fast as they could” at a triage center outside the emergency ward, he added. But the nation is not equipped for a mass casualty event, McGarry said.

Video shared by the Vanuatu Broadcasting and Television Corporation showed crowds outside the hospital. Phone numbers for the police, the hospital and other public agencies did not connect.

A video posted on social media appeared to show crumpled buildings in Port Vila, including one that had collapsed onto its lower floors and cars parked on the street below. Amanda Laithwaite said her husband was among a group of rescuers attempting to shift the roof of the three-story building because they believed people were trapped inside, but their progress was slow without specialist machinery.

Elsewhere, a building housing a number of diplomatic missions in Port Vila — including those of the United States, Britain, France and New Zealand — was significantly damaged, several of its tenants said. But there were no reports of embassy staff unaccounted for.

Buckled windows and debris

The U.S. Embassy’s Facebook page said all staff were safe, but the building was closed until further notice. The office had only opened in July, as part of a wider push by the U.S. to expand its Pacific presence in order to counter China’s burgeoning influence on governments in the region.

Australia’s foreign ministry also said its workers were safe.

A video on social media showed 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 some roads.

“We haven’t heard at the moment about any casualties, but I will be shocked if we don’t hear that bad news coming through from Port Vila at some point,” Katie Greenwood, the Fiji-based head of the Asia-Pacific regional office for the Red Cross, told the Australian Broadcasting Corp.

All flights grounded

McGarry said a “massive landslide” at the international shipping terminal was likely to impede the country’s recovery. The airport’s runway is also damaged, he said.

Port Vila’s airport could not be contacted on Tuesday, but flight tracking sites suggested all flights were grounded. Some airlines in Australia and the Pacific said they had cancelled or paused flights scheduled for Wednesday and were awaiting news of the airport’s status.

Australian Foreign Minister Penny Wong told reporters that her country would provide whatever help was needed. New Zealand’s Foreign Minister Winston Peters said 45 New Zealanders were registered as being in Vanuatu and his government was “deeply concerned” about the situation there.

Vanuatu has been led by four prime ministers in four years and is due to go to the polls in January for a snap election. In November, Prime Minister Charlot Salwai asked President Nikenike Vurobaravu to dissolve Parliament so he did not have to face a no-confidence vote as his recent predecessors did.

But Vanuatu is accustomed to natural disasters, including havoc wrought by cyclones and volcanic eruptions. Its position on a subduction zone — where the Indo-Australia tectonic plate moves beneath the Pacific Plate — means earthquakes of greater than magnitude 6 are not uncommon and the country’s buildings are intended to withstand quake damage.

Associated Press writer Rod McGuirk in Melbourne, Australia, contributed to this report.