Philippines President Rodrigo Duterte says a deadly casino attack in Manila was not the work of the Islamic State (IS) group and the gunman was "crazy".

Key points: President Duterte declares attacker was just "crazy"

President Duterte declares attacker was just "crazy" "Clear example" of "lone wolf" attack, politician Alvarez says

"Clear example" of "lone wolf" attack, politician Alvarez says Politician says attack should serve as a "wake-up call"

Mr Duterte made the remarks — his first comments on the attack — on Saturday in the southern Philippines.

A gunman entered the Resorts World Manila complex early on Friday and set fire to the gambling tables, unleashing smoke that killed 37 patrons and casino employees.

He fled with $2.69 million in stolen casino chips, then killed himself in a hotel room after being shot by security officers at the Resorts World Manila entertainment complex, police said.

Mr Duterte said the attacker was "crazy" because he stole casino chips, even though he would not be able to use them.

He said the IS attacks were "more cruel and brutal".

"They would just simply kill people for nothing. Not even for a reason," he said.

"And that's the reason why the world today has banded together to fight this scourge of terrorism, especially if you kill in the name of God. There is no rhyme or reason really."

A second "person of interest" who was in the casino at the time is cooperating with the investigation, police said.

The attacker killed more than 30 people. ( AP: Philippine National Police )

Mr Duterte's comments are aligned with earlier police statements regarding the attacker's motive, but contradict the comments of top Philippines politician Pantaleon Alvarez, who said the gunman was a "lone wolf" terrorist.

Mr Alvarez, speaker of the lower house of Congress and a close ally of President Duterte, said on Saturday 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," Mr Alvarez said in a statement.

The IS group claimed responsibility for the attack, but that was rejected by Philippines officials, who said it appeared to have been a botched robbery.

Mr Duterte's spokesman, Ernesto Abella, said on Friday there was no proof linking it to a protracted urban battle between government troops and Islamist militants in the country's south.

"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," Mr Alvarez said.

The Philippines has been on heightened alert amid a crisis in the city of Marawi, on the southern island of Mindanao, where troops have been battling Islamist rebels since May 23 and martial law is in place.

Wake-up call for law enforcement, security

Sorry, this video has expired Smoke billows from the Resorts World building in Manila. (Photo: Reuters/Erik De Castro)

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 blaze, smoke from which 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 have also corrected earlier statements about the attacker.

They originally said he arrived at the hotel in a 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," Mr 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."