Explosions and gunfire has been heard at Resorts World Manila, according to local reports.
The hotel and casino complex, situated near the city’s international airport, is currently on lockdown following “gunfire from unidentified men”.
The company has asked “for your prayers during these difficult times.”
AFP news agency said the so-called Islamic State has claimed responsibility for the attack.
Videos emerging from the scene showed emergency services outside the complex in the Pasay City area of metro Manila.
A witness told NBC News “there are quite a few injuries” after the incident.
The US has issued travel advice to avoid the area and monitor local news.