Ronald dela Rosa, director general of the national police, said his officers exchanged fire with the gunman early Friday as he hid inside the hotel.
Dela Rosa said the suspect covered himself with blanket, used gasoline to torch himself.
Al Jazeera's Jamela Alindogan, reporting from southern Philippines, cautioned that the group has a history of claiming responsibility for incidents, which later turned out to be unrelated local crimes.
"I would like to begin by addressing the terrorist attack in Manila", Trump said at the start of his speech on Thursday.
The gunman parked his auto at the second floor of the building, started firing in the air and burned some tables before entering the storage room.
The man left the room and went upstairs to the hotel section, but left the backpack near the stock room, according to Dela Rosa.
The police chief said that the suspected gunman was later found dead in a hotel room after apparently committing suicide.
According to Dela Rosa, a single gunman wielding an assault rifle entered the gaming area, fired shots that were not directed at individuals in the room, and set gambling tables on fire with gasoline.
Kimberly Molitas, a spokeswoman for the capital's police office, said $2.27m worth of casino chips stolen during the raid had been recovered.
He said the man then fired again at a stock room containing gambling chips and filled a backpack with them.
Heavily-armed SWAT officers wearing bulletproof vests and body armor descended on the scene, Camille Abadicio of CNN Philippines said.More news: Philippine Casino Locked Down Amid Reports of Gunfire
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Mr Dela Rosa also said it was clear he was not a terrorist and instead possibly a "sore loser".
About 90 minutes after the attack began, Resorts World Manila said on its Facebook page that it was on lockdown following reports of gunfire and it was working to ensure the safety of guests and workers.
"He's dead. He was killed by our troops", Dela Rosa had told the GMA television network.
The police chief confirmed his original statement to the AP that there is "no concrete evidence that the attack was terrorism" - despite President Trump's opening remarks while announcing the US withdrawal from the Paris accord on climate change.
Local news media reported that explosions had been heard coming from the vicinity of the hotel, which is across a road from the city's worldwide airport.
The PNP is yet to give information as to how may were hurt in the incident or is there any casualties but Molitas said they are in close coordination with the Bureau of Fire Protection and medical and rescue teams to address the situation.
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.
Police said the gunman was tall with a pale complexion and spoke English.
Resorts World Manila features multiple hotels and bars, as well as a shopping centre and casino.
With an Islamist insurgency flaring in the Philippine city of Marawi, the initial assumption of both visitors and the media was a jihadist attack. It is really sad with what's going on throughout the world with terror.
Trump says, "Our thoughts and our prayers and with all of those affected".