CNN Philippines reports a masked gunman began firing on guests and hotel employees fleeing the scene at the Resorts World Manila complex.
A witness said the incident started around midnight local time Thursday.
It is not immediately clear how many people were killed or injured in the possible attack. The nature of the incident is also unclear, as emergency personnel said they have treated people for smoke inhalation and other injuries, but not for gunshot wounds.
So far, no one has claimed responsibility for the incident.
The Philippines has been battling numerous incidents ISIS-linked terrorism, particularly on the southern island of Mindano, where Philippine President Rodrigo Duterte declared martial law over the island.
This is a breaking news story. Check back for updates.
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