Rescue workers struggled Wednesday to reach isolated communities on a popular Philippine tourist island that was devastated by a huge earthquake, as aftershocks tormented survivors and the death toll surpassed 140.

The 7.1-magnitude earthquake smashed the central island of Bohol on Tuesday morning, ripping apart bridges, tearing down centuries-old churches and triggering landslides that engulfed entire homes.

The number of people confirmed killed on Bohol and neighbouring islands climbed from 93 overnight to 142 on Wednesday afternoon, and more bad news was expected as rescue workers reached some of the hardest-hit areas.

"Our efforts today are focused on reaching isolated areas. We suspect individuals are trapped out there and we have to conduct search and rescue," National Disaster Risk Reduction and Management Council spokesman Reynaldo Balido told AFP.

With destroyed bridges, ripped-open roads and power outages fragmenting the island of about one million people, Balido said it was proving difficult for police and government rescue workers to reach isolated communities.

At Loon, a small coastal town of about 40,000 people just 20 kilometres (12 miles) from the epicentre of the earthquake, shocked survivors wandered around the rubble of collapsed buildings looking for relatives.

Farmer Serafin Megallen said he dug with his hands, brick-by-brick, to retrieve his mother-in-law and cousin from the rubble of their home on Tuesday.

"They were alive but they died of their injuries three hours later. There was no rescue that came, we had to rely on neighbours for help," he told AFP.

Megallen said a neighbour with a truck tried to drive the bodies to Loon's funeral parlour, only to find out the bridge across a river on the way was destroyed.

The bodies were then taken across the river aboard a boat.

"But no one will give them last rites because the church was also destroyed," he said.

Ten churches, many of them dating back centuries to Spanish colonial rule of the Philippines, were destroyed or badly damaged on Bohol and the neighbouring island of Cebu.

Loon's limestone Our Lady of Light church was reduced to mounds of crushed rocks.