Rescuers dug through rubble Saturday to find survivors after a powerful earthquake struck the southern Philippines, killing at least six people and sending thousands fleeing for safety.

Residents of the southern town of Surigao in Mindanao island spent the night huddled in fear as aftershocks rocked the city following the 6.5-magnitude quake which struck late Friday when many people were already in bed.

Provincial disaster management officer Ramon Gotinga said that most of those killed had died due to falling objects.

But he added that one elderly man was buried in his home when the upper floor collapsed, and despite rescue teams digging throughout the night, they were unable to recover him alive.

Another 80-year-old woman died of a heart attack, Gotinga said, adding that at least 126 people were injured, 15 of them in a serious condition.

The quake damaged many buildings, including in the two-storey Gaisano mall -- one of the city's largest structures -- and shattered windows, sending sharp shards and heavy rubble into the street.

One bridge collapsed and two others were damaged in the quake, which also cracked the city airport's runway, forcing flights to be diverted, the civil defence office added.

"I thought it was the end of the world. The cement on the roads was cracking open," resident Carlos Canseco told ABS-CBN television.

Thousands of terrified residents fled their homes with many running to higher ground, fearing that a tsunami would hit the coastal city of over 152,000 people.

Regional civil defence chief Rosauro Arnel Gonzales said several houses had collapsed and search and rescue teams had been dispatched to make sure no one was inside.

"There are reports of houses that were damaged and they (the rescue teams) have to go around these impacted areas to really ascertain whether there is a need to conduct a rescue," he told AFP.

The disaster also knocked out both power and water services in Surigao City and surrounding areas.

Authorities said they expected power to be restored by Sunday but that it may take as much as three days to bring back water services.

- Mass hysteria -

Many residents spent the night in parking lots and open fields to avoid falling objects or collapsing buildings.

Hospital staff temporarily brought bed-ridden patients outside until the aftershocks eased.

Local journalist Roel Catoto said when he visited a hospital emergency room after the quake, what he found was "mass hysteria."

"There were a lot of wounded patients coming in and all the patients who were (already) confined were rushing outside. They were afraid the hospital would collapse," he told AFP.

Gotinga said residents were still on edge on Saturday.

"They are all still traumatised. At the slightest shaking, they run out in the streets," he said.

President Rodrigo Duterte's spokesman Ernesto Abella assured the public that the government was ready to assist them.

"These are trying times and our hearts go out to Surigao," he told reporters.

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

The last lethal quake that hit the country measured 7.1-magnitude. It left over 220 people dead and destroyed historic churches when it struck the central islands in October 2013.