Rescuers say they have expanded a search for trapped survivors in quake-rocked Vanuatu to "numerous places of collapse" beyond the capital, as the reported death toll climbs to 10.

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.