Mr de la Rosa said: "Don't panic, this is not a cause for alarm". We are just alert.
"It's either he lost in the casino and wanted to recoup his losses or he went totally nuts", police chief Oscar Albayalde said.
Several of the deceased died due to smoke inhalation and suffocation even as guests and the staff tried to escape from the premises of the resort, Reuters reported citing ANC News channel, which quoted sources from the Bureau of Fire Protection.
"The lone gunman is already neutralized; he's dead".
The incident initially raised fears of a connection to fighting on the southern island of Mindanao between security forces and Islamist rebels linked to the Islamic State, who have taken hostages and burned buildings in a battle for control of the city of Marawi.
After the hours-long attack at Resorts World Manila, Philippine National Police Chief Ronald Dela Rosa told reporters that a single gunman responsible for the assault used gasoline to set fire to gambling tables but did not fire at people.
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.
The gunman, described as six-foot tall, foreign-looking with a mustache, had managed to elude police forces for almost six hours before he locked himself inside Room 510.
The PNP Chief also said fire in the hotel is declared fire out but is still locked down by police as investigation continues and clearing operations are still ongoing. "There is no element of violence, threat or intimidation that leads to terrorism", Dela Rosa said.
Resorts World Manila said on social media it was in lockdown.
"They can claim anything as part of their propaganda but we have to base our conclusion on evidence", he stressed.
"We see no terrorism in this act", the spokesperson said. "I don't know if she is still there". She was not moving and was probably dead.
About 90 minutes after the attack began, Resorts World Manila said in its Facebook account that it was "currently on lockdown following reports of gunfire from unidentified men", adding, "the company is working closely with the Philippine National Police to ensure that all guests and employees are safe".
"We ask for your prayers during these hard times", the resort tweeted.
"There were other gunmen because we can hear gunshots elsewhere", he told Manila radio station DZMM.
"I heard many, many gunshots", witness Julio Silva said, citing that she also heard a SWAT member shouting that they'd been hit. The White House said President Donald Trump is aware of the situation and is being briefed with updates.
The Islamic State has claimed responsibility for the attack, AFP reported.
IS said "lonewolf soldiers" from its group carried out the attack, according to the SITE Intelligence Group that monitors terrorist organisations.
A lone gunman stormed a casino in Pasay City shortly after midnight armed with a baby armalite, fired at the stock room of chips, carted away with P113 million worth of it, and was later found dead inside one of the hotel's rooms on Friday morning.