Most of the victims died from suffocating in thick smoke.

President Rodrigo Duterte's spokesman, Ernesto Abella, said that the attack could not be linked to fighting between government troops and Islamist militants in the country's south.

He said that there was no evidence to validate this.

"All indications point to a criminal act by an apparently emotionally disturbed individual," Abella told a media conference.

"Although the perpetrator gave warning shots, there apparently was no indication that he wanted to do harm or shoot anyone."

Police said the gunman killed himself soon after the attack, and they later announced they were looking for a second "person of interest" who was believed to be a Philippine national.

Chief of the capital's police office, Oscar Albayalde, said those that died were in the casino's main gaming area.

"What caused their deaths is the thick smoke," he told reporters. "The room was carpeted and of course the tables, highly combustible."

An official of the Resorts World Manila said the dead included 13 employees and 22 guests.