Gunshots and explosions erupted after midnight in a hotel and casino complex near Manila's airport, sending hundreds fleeing into darkened streets early Friday in chaos that appeared linked to a Muslim militant siege in the country's south.
The Islamic State group, in a quick communique, took responsibility for the attack.
Philippine police rushed to the Resorts World Manila complex early Friday after gunshots rang out and witnesses reported gunmen barging in at a mall in the commercial center, where whitish smoke began billowing from an upper floor.
Witnesses reported seeing injured people, including a SWAT member, who rushed to the scene and was reportedly fired upon by unidentified men. It was not immediately clear if anyone was killed, or if the attack had concluded.
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 difficult times," the company said.
Philippine police have not given details about the incident but have begun cordoning off the area near the Ninoy Aquino International Airport.
"I heard many, many gunshots," Julio Silva, a casino player who managed to dash out of the mall complex amid the gunfire, told DZMM radio network.
Mr. Silva said he saw a SWAT member who was shouting "I was hit, I was hit."
A DZMM radio reporter on the scene said she saw two ambulances ferrying two people away, one with a bandage on the leg and another in wheelchair.
As news of the attack spread, President Trump offered the thoughts and prayers of the American people to the Philippines.
"It is really very sad as to what's going on throughout the world with terror," he said from the White House Rose Garden. He said he is "closely monitoring the situation" and will continue to provide updates.
The violence is unfolding amid a 10-day deadly siege by Muslim militants aligned to the Islamic State group in the southern city of Marawi. The attack has sparked fears that the militants may attack elsewhere to divert the focus of thousands of troops trying to quell the siege.
The SITE Intelligence Group, a US terrorism monitor, said an Islamic State-linked Filipino operative who provides daily updates on the ongoing clashes in Marawi, claimed that "lone wolf soldiers" of the Islamic State group were responsible for the attack at Resorts World Manila.
An English message by the operative was distributed across several pro-IS Telegram chat groups, SITE said. According to SITE, he wrote: "The lone wolf soldiers of Khilafah attack the heart of Kufar the city of Manila in Resort World."
President Rodrigo Duterte sent soldiers to the southern Philippines to end the siege by about 500 militants. Officials say 120 militants and at least 25 soldiers, five policemen and two dozen civilians have been killed in the fighting since Tuesday last week.
Mr. Duterte declared martial law in the Mindanao region, the southern third of the Philippines, to crush the insurrection, and poured in troops backed by airstrikes, artillery fire and armored vehicles.
The unrest has boosted fears that the Islamic State group's violent ideology is gaining a foothold in the country's restive southern islands, where Muslim separatist rebellions have raged for nearly half a century.