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 from the epicentre of the earthquake, shocked survivors wandered around the rubble of collapsed buildings looking for relatives.

The only people involved in the search and rescue efforts on Wednesday morning at Loon were residents and local police, who themselves had lost their homes or relatives.

They struggled as aftershocks continued to rattle the area. More than 800 aftershocks were recorded, including two on Wednesday with magnitudes exceeding 5.1, according to national disaster authorities.

President Benigno Aquino visited Bohol on Wednesday to oversee rescue efforts, and sought to reassure survivors.

"The bottom line is we do not have to fear that something stronger than... (Tuesday's quake) is coming," Aquino said in a nationally televised meeting with cabinet members at Tagbilaran, Bohol's capital.

Most of the deaths were on Bohol, which is one of the most popular tourist islands in the Philippines because of its beautiful beaches, rolling "Chocolate Hills" and tiny "tarsier" primates.

The number of confirmed fatalities on Bohol jumped to 132 as authorities in isolated towns restored communications and reported dozens more deaths, the head of the province's information office, Augustus Escobia, told AFP.

But he said reports had still not come in from one town close to the epicentre that was believed to be badly damaged.

Nine people died on neighbouring Cebu island, home to the Philippines' second-biggest city of the same name, while another person was confirmed killed on nearby Siquijor island.

The Philippines lies on the so-called Ring of Fire, a vast Pacific Ocean region where many earthquakes and volcanic eruptions occur.

The deadliest recorded natural disaster in the Philippines occurred in 1976, when a tsunami triggered by a 7.9-magnitude earthquake devastated the Moro Gulf on the southern island of Mindanao.

Between 5,000 and 8,000 people were killed, according to official estimates.