Just after midnight on Friday local time, a man burst into the Resorts World building near Manila's global airport.
Most of the dead appear to have suffocated from thick smoke after the man set fire to casino tables, sources told local media.
The police in Manila is still trying to establish the identity and affiliation of the gunman who set himself alight after the incident.
ISIS later provided the gunman's "nom de guerre" and said he killed and injured almost 100 "Christians" during the rampage. Police say that 37 people died in the fire, most likely from suffocation.
US President Donald Trump Thursday expressed sadness and sympathy for victims of what he labelled a "terrorist attack".
Metropolitan Manila Police Chief Oscar Alabayade said Saturday that the driver took the suspect to the casino.
The gunman, described by Mr dela Rosa as white, with a moustache, about 6ft and English speaking, fled the gambling area and barged into a room on the fifth floor of Maxims Hotel, which is part of the Resorts complex.
This story has been corrected to show that the dollar value of the stolen chips was more than $2 million, not $200,000.
Ronald Romualdo, a maintenance worker at Resorts World, said he and his colleagues heard gunshots and saw people smashing the windows on the second floor and third floor to escape.
Police had previously said on multiple occasions that the attack was not related to terrorism.
All this on a week that has seen the Philippine military battle ISIL-aligned militants in the country's south. Albayalde said "the bodies were found in the gaming area of the casino". Police said there were no confirmed reports of gunshot wounds.
Philippine national police Chief Dela Rosa told local radio station DZMM radio "Don't panic, this is not a cause for alarm".
"Given the volatile security situation in Marawi the killing of 36 people in the casino is worrying", said Abdul Basit, Associate Research Fellow at the S. Rajaratnam School of International Studies in Singapore.
"This is not an act of terror".
Dela Rosa told reporters at the scene that the gunman stole gambling chips, shot an LED monitor and set ablaze gambling tables by pouring gasoline on them.
A statement from ISIS stated an Islamic State fighter, identified as Abou al-Kheir al-Arkhebieli, was the gunman.
The body of the gunman was found in a hotel room inside the complex about five hours later, Dela Rosa said.
Like most Manila casinos and hotels, Resorts World had metal detectors at its entrances and typically checked vehicles before allowing them access.
Fox News reported that at least 25 people were injured in the shooting and explosions that rocked the resort complex in Pasay City after midnight.