According to police sources, the incident is being termed as a botched robbery attempt and the gunman was said to be acting alone.
Though no one immediately claimed responsibility for the incident in Pasay, it came as the Philippine military has been battling Islamic State-linked militants in the southern city of Marawi.
MALAYSIAN gaming conglomerate Genting Group has slammed last night's attack on its casino in Manila as a "cowardly act" and said its security team is working with local authorities to conduct search and rescue operations on its building where so far, 37 bodies including the suspect, have been found. According to Newsweek, eyewitnesses said they saw a "tall, foreign white man" before chaos descended, casting some suspicion on the gunman's nationality and ethnicity.
Police in the country's capital said the man did not aim his assault rifle at people and appeared to just be interested in the robbery. "He only went for the casino chips".
But hours later, the Islamic State group claimed responsibility in a statement, saying "Brother Abu al-Kheir al-Arkhabili was able to immerse among a gathering of Christian fighters in the Resorts World Manila in Manila where he carried out killing and hurting until he died as a martyr". "Although the perpetrator gave warning shots, there apparently was no indication that he wanted to do harm or shoot anyone".
"They can always claim whatever they want to claim", said Oscar Albayalde, police chief for the Manila area. The room was carpeted and the tables were combustible, he said, and all the bodies were found in the smoky gambling room.
Police said that the armed suspect, who is yet to be identified, forced his way into the casino around midnight local time, and started shooting at gambling machines and setting tables on fire.
Philippine police don't have any evidence that gunfire at a popular resort area was terror related.
"He lay down on the bed, covered himself with a thick blanket, apparently poured gasoline on the blanket and burned himself", Dela Rosa said.More news: Justice Department Turns to High Court to Reinstate Travel Ban
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This image made from closed circuit television made available by the Philippine National Police on Friday, June 2, 2017, shows the gunman at the Resorts World Manila complex in Manila, Philippines.
Ronald Romualdo, a maintenance worker at Resorts World, told the station he saw a woman fall from an upper floor while trying to escape.
"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.
"As far the PNP is concerned we can not yet attribute this to terrorism".
"He would have shot all the people gambling there" if it had been terrorism, national police chief Ronald dela Rosa said.
Resort owner Travellers International Hotel Group Inc said authorities were still seeking details.
He said the man then fired again at a stock room containing gambling chips and filled a backpack with chips worth 113 million pesos ($2.3 million).
The road that runs along the front of the building was restricted to emergency vehicles and those taking away the dead.
Jeri Ann Santiago, who works in the emergency room at the San Juan de Dios hospital, said patients were suffering from smoke inhalation and some had fractures. Police said there were no confirmed reports of gunshot wounds.