Thirty-four bodies were found inside a casino in Philippines' capital city Manila, after it was attacked by a lone gunman in the early hours of Friday, police said.

The victims did not appear to have been shot, but indications were that they had suffocated, a senior police official told CNN Philippines.

A probe to identify the victims and the cause of their death is on.

The incident unfolded when the gunman forced his way into the Resorts World Manila casino, shot at gambling machines and set tables on fire.

The man then proceeded to ransack a room and stole gaming chips, Philippines National Police Chief Ronald Dela Rosa said. 

He stuffed chips totalling 113 million pesos ($2 million) in a backpack, but it was recovered by police.

Earlier reports suggested the gunman had been shot, but police later confirmed that he had committed suicide by setting himself on fire, reports CNN.

"He committed suicide by setting himself on fire in one of the rooms on the fifth floor of the Resort World Hotel," the National Capitol Region Police Chief Oscar Albayalde told the media here.

The attacker was found in the room, burned beyond recognition, next to a machine gun and a pistol.

The gunman did not appear to be firing at people, said Dela Rosa, which suggested the incident was not terror-related.

"It's too early to tell," he added.

Hundreds of guests and employees rushed out of the resort hotel as soon as the gunman began shooting, CNN reported.

Video captured people fleeing, the sound of gunshots and smoke coming from the upper floors of buildings.

Resorts World Manila, also known as RWM, is a resort complex in Newport City, a residential and commercial centre in metropolitan Manila.

The complex, which is described on RWM's website as "the first and largest integrated resort in the Philippines," is across from Ninoy Aquino International Airport.

All terminals at the airport were placed on lock-down following the attack.