"It was the most violent earthquake I've experienced in my 21 years living in Vanuatu and in the Pacific Islands. I've seen a lot of large earthquakes, never one like this," he said.
The road connecting Port Vila to the international shipping terminal was blocked by landslides, he added.
Other footage posted on social media showed buckled windows and collapsed concrete pillars on a building hosting foreign missions in the capital, including the U.S., British, French and New Zealand embassies.
7.7 magnitude earthquake in far Pacific creates small tsunami o...
A spokesperson for the U.S. Embassy in Papua New Guinea said its embassy in Port Vila had sustained "considerable damage" and was closed until further notice.
New Zealand's High Commission building, which is co-located with the U.S., French and British missions, had "sustained significant damage," a foreign ministry spokesperson said in a statement.
There were communications outages across the country, the New Zealand statement added, while the Australian High Commission in Vanuatu said its communication systems had also been affected.
Reuters was not able to immediately able to confirm the casualty figures, with authorities in Vanuatu not reachable for comment.
The U.S. Geological Survey (USGS) said the quake was at a depth of 10 km (6.2 miles).
Half a dozen aftershocks hit Vanuatu following the initial quake, USGS data showed.
Several were heavy enough to be felt in Port Vila, McGarry said.
"There was one that had us all sort of perched and ready to move again. But none of them have been anywhere near as bad as the initial shock," he said.
Earlier, the U.S. Tsunami Warning System cancelled an initial tsunami warning for Vanuatu.
Authorities in the U.S., Australia and New Zealand said there was no tsunami threat to their territories.
Australia's Foreign Minister Penny Wong said Australia was closely monitoring the situation following the "devastating earthquake".
"We stand ready to support Vanuatu, as the extent of the damage is assessed. Vanuatu is family and we will always be there in times of need," she said in a statement.