MANILA - At least 45 people were killed after a military transport plane carrying mostly soldiers being deployed to fight Muslim extremists in the southern Philippines crashed on Sunday (July 4) in war-torn Sulu province, a stronghold of the Abu Sayyaf terrorist group.

Forty-nine others were rescued, but five more remain missing, the army's Joint Task Force Sulu said in a statement.

Three people on the ground who were on the plane's crash path were among those who died.

"We remain hopeful that we can find more survivors," the task force said.

This may well be the worst peacetime disaster to hit the Philippine Air Force.

General Cirilito Sobejana, the military chief, said the Hercules C-130 transport plane, with tail number 5125, crashed at around 11.30am as it was trying to land on a small runway in Patikul town in Sulu.

"It missed the runway while trying to regain power," said Gen Sobejana.

Defence Minister Delfin Lorenzana told Reuters the plane had been carrying at least 92 people, including three pilots and five other crew members, according to his initial reports.

"Responders are at the site now. We are praying we can save more lives," said Gen Sobejana.

Photos posted on social media showed the plane engulfed in flames and billowing smoke.

The plane came from Manila, where it had a senior officer, Major-General Romeo Brawner Jr, and his staff as passengers.

It made a stop in Cagayan de Oro City, where it picked up troops who had just been on a six-month basic training course. Most of the soldiers were privates assigned to the 4th Infantry Division.

Maj-Gen Brawner met the soldiers and gave them a send-off, as he was set to assume command of the division this week. He did not board the plane when it left for Sulu.

The military has a heavy presence in southern Philippines where militant groups, including the kidnap-for-ransom outfit Abu Sayyaf, operate.

The plane in Sunday's incident was also carrying five military vehicles.

Major-General Edgard Arevalo, a spokesman for the military, said it had ruled out the possibility that the plane had been fired upon as it was landing.

"We are ruling out an attack… What we know so far is that it developed a problem as it was making its approach. There was an attempt to recover, but it ran out of power," he said.

The C-130 Hercules is an American-built turboprop that is commonly used by militaries around the world, and is sometimes kept in service for decades.

The plane that crashed was handed over by the United States to the Philippines in January.

The Philippines military has been modernising its air force, to deal with threats from terrorists at home and challenges posed by China in disputed waters.

Earlier this month, a newly acquired Black Hawk helicopter crashed during a training flight. Six died in that incident.

"I have ordered a full investigation to get to the bottom of the incident, as soon as the rescue and recovery operation is completed," said Mr Lorenzana, the defence chief.

He sought to douse speculation that the military's recent arms purchases from the US could be "defective".

"With the investigations of the past mishaps still ongoing, such speculation is as yet baseless and disrespectful to the affected men and women of the Philippine Air Force, (Armed Forces) and their families," he said.

President Rodrigo Duterte has yet to issue an official statement, but his spokesman Harry Roque said: "We are deeply saddened by the mishap."

US Charge d'Affaires John Law also offered his government's "sincerest condolences" to the families of those who died.