"It was quite a significant earthquake, and we're still having a few aftershocks," Ben McKenzie of the New Zealand High Commission told The Associated Press by phone from Port Vila.
The quake hit about 25 miles (40 kilometers) northwest of Port Vila at a depth of 22 miles (35 kilometers), the U.S. Geological Survey said.
Police spokesman John Frat told the AP that officials had not received any reports of injuries or major damage, but described the temblor as "a very sharp quake — it was the worst I have felt in my life."
"Many people left the center of town and went to higher places, fearing a tsunami," he said by telephone from Port Vila. "We're still experiencing sharp aftershocks and all communications were lost for a time, but things are coming back to normal now."
The four-story office building housing the New Zealand High Commission suffered some damage, said McKenzie, first secretary at the New Zealand diplomatic post. Office shelves and ceiling tiles fell down and computers were "thrown across the office" by the jolt, he said.
"We're trying to ensure everybody is safe and we're evacuating the building" to check that it's not "structurally damaged," he said.
Joel Pari, a worker at Port Vila's Trading Post newspaper, said they had not heard any reports of injury or major damage following the quake.
"But it was really strong — it really shook the buildings and everybody fled outside and to higher ground in case of a tsunami," he said.
Roland Cowles, manager of Sunset Bungalows waterfront resort at Port Vila, said his wife Jenny suffered minor cuts as she fled a supermarket.
"For a good 10 seconds, you almost couldn't walk — it was throwing you around that much and people in the supermarket had to be evacuated because of all of the damage that was being done," he told Ten Network television news in Australia by telephone.
Vanuatu is part of the Pacific "ring of fire" — an arc of earthquake and volcanic zones stretching from Chile in South America through Alaska and down through the South Pacific.