Philippine President Rodrigo Duterte said on Saturday that Islamic State militants were not behind the attack on a casino in the capital that killed at least 36 people, supporting a police assessment that it was merely a botched robbery.

The gunman who burst into the Resorts World Manila entertainment complex early on Friday, firing shots, setting gaming tables alight and killing dozens, all suffocating in thick smoke, had been labelled by a top lawmaker as a "lone wolf" terrorist.

"That is not the work of ISIS," Duterte, using an acronym for Islamic State, told reporters in Cagayan de Oro city where he was visiting troops. "The work of ISIS is more cruel and brutal, they would simply kill people for nothing."

Clips from the casino CCTV, which police and officials at Resorts World released on Saturday, showed the gunman was firing shots at the ceiling and setting gaming tables and slot machines ablaze.

The gunman, whose identity remains unknown, was caught on camera purportedly stealing casino chips worth 113 million pesos($2.27 million) from a storage room before he was later found by security officers, who shot and wounded him during an exchange of fire.

"Why would you steal plastic you won't be able to use?" Duterte said. "That guy is crazy."

But Pantaleon Alvarez, speaker of the lower house of Congress and a close ally Duterte, said he was not convinced the incident was a criminal case of armed robbery and arson.

"This is a clear example of a 'lone wolf' terrorist attack targeting civilians to inflict maximum loss of life and damage to property, as what has happened in other countries," Alvarez said in a statement.

Duterte's spokesman, Ernesto Abella, said on Friday there was no proof linking the casino attack to a protracted urban battle between government troops and Islamist militants in the country's south. His security adviser, Hermogenes Esperon, said all the evidence pointed to an attempt to steal casino chips.

"We must draw up a clear and better plan to secure Metro Manila and other urban centres from IS-linked groups that we already know will attempt to kill and maim in pursuit of their jihadist ideology," Alvarez said.

The stolen chips have been recovered.

Police said on Saturday there were two "persons of interest" who have connections with the gunman and are cooperating with the investigation.

WAKE-UP CALL

The attack at the casino hotel complex, which is close to an airport terminal and air force base, lasted more than six hours.

Security experts and patrons at the casino on Friday expressed alarm at the apparent ease with which a lone gunman was able to enter the building, open fire and start a fire whose smoke killed more than 30 people.

Firefighters discovered the bodies in the main gaming area, hours after the country's police chief had said the situation was under control.

Police corrected earlier statements about the attacker.

They originally said he arrived at the hotel in a private car, but changed that to a cab, and they had described him as Caucasian and English-speaking but the cab driver told them he spoke in the local language.

"Our authorities should get their act together and put in place the highest level of security measures to prevent this from happening again, here or elsewhere in the country," Alvarez said.

"This incident should be a wake-up call for the police and the military to cooperate closely in making the seat of government and our financial and business centre safe from any terrorist attack."