At least 31 people have been killed and 40 rescued in the crash of a Philippine air force C-130 aircraft carrying troops in a southern province, Philippine Defense Secretary Delfin Lorenzana said on Sunday, while 17 people remain missing.

The secretary added that rescue efforts are ongoing.

The dead were 29 soldiers aboard the plane, and two civilians who were on the ground on Jolo island, 1,000 kilometers south of Manila, said Arsenio Andolong, spokesperson for the Department of Defense.

He said the aircraft had 92 people on board, including three pilots and five crew.

The rest were army personnel.

The plane was transporting troops from southern Cagayan de Oro city, Chief of Staff Gen. Cirilito Sobejana said. Government forces have been battling Abu Sayyaf terrorist group in the province of Sulu for decades.

"It’s very unfortunate," Sobejana told reporters. "The plane missed the runway and it was trying to regain power but failed and crashed."

Sobejana said at least 40 people on board were brought to a hospital and troops were trying to save the rest.

It was not immediately clear what caused the crash.

It has been raining in the central Philippines but it was not immediately clear if the weather in the Sulu region has been affected.

The airport in Sulu’s main town of Jolo is located a few kilometers from a mountainous area where troops have battled the Abu Sayyaf.

Some militants have aligned themselves with the Daesh terrorists.

The United States and the Philippines have separately blacklisted the Abu Sayyaf as a terrorist organization for bombings, ransom kidnappings and beheadings.

It has been considerably weakened by years of government offensives but remains a threat.