MANILA, Philippines (AP) — Philippine authorities on Monday prepared to send a search mission near the crater of a restive volcano after they spotted the suspected wreckage of a small plane that went missing with four people on board over the weekend.

Two Filipino pilots and two Australians were aboard the Cessna 340, which lost contact after takeoff from Albay province southeast of the capital Saturday morning on its way to Manila, the Civil Aviation Authority of the Philippines said.

The Australians were working as consultants for Energy Development Corp., a large geothermal power company. The company said it has deployed teams backed by helicopters and drones to help in the search.

“We will not stop until they are found,” company official Allan Barcena said.

Mayor Carlos Baldo of Albay’s Camalig town and other officials told reporters Sunday that an aerial search spotted the suspected wreckage, including the tail, scattered about 1,150 feet (350 metres) from the crater on the steep southwestern slope of Mayon Volcano. There was no sign of people.

A ground search was hampered by rainy weather over the weekend.

About 60 search and rescue personnel may scale the 8,077-foot (2,462-metre) Mayon when the weather clears, Baldo said. They’ll also need assistance from volcano experts and local officials because of the restiveness of Mayon, one of the country’s 24 active volcanoes.

“It’s a very risky operation,” Philippine Institute of Volcanology and Seismology director Teresito Bacolcol told The Associated Press. “It’s a race against time and it’s a matter of life and death but there’s also the danger of rockfalls and volcanic lahar.”

Villagers are normally prohibited from entering a permanent danger zone six kilometres (3.7 miles) around the volcano.

“There is no other missing plane in the area and there’s testimony from residents, who saw the plane flying unusually low before they heard an explosion,” Baldo told AP by telephone.

He said a chopper could drop the rescuers nearer to the suspected crash site.

A popular tourist attraction because of its near-perfect cone, Mayon last erupted in 2018, displacing tens of thousands of villagers.

It’s currently under the second of five volcano alert levels, meaning volcanic earthquakes, steam and gas emissions, ground deformation and intermittent ash and steam blasts have been sporadically detected. Alert five means a major and deadly volcanic eruption is underway.

Separately, a single-engine Cessna plane that went missing January 24 with six people on board in the northern Philippine province of Isabela has not yet been found. Officials said a search for the plane was continuing on and off, depending on the weather.