|Resorts World in Manila has four hotels, a shopping centre and restaurants|
"I live right behind Resorts World ... and you can see the smoke and hear gunshots and people are shouting at each other," one witness said in a video posted on Facebook.
Swat teams and ambulances have reportedly been sent to the scene.
ABS-CBN News reported that several injured people had been seen at Resorts World, but there are not official casualty figures yet.
The Metro Manila Development Authority confirmed a fire had broken out.
The complex, opposite the Ninoy Aquino International Airport, includes four hotels, casinos, a shopping centre, cinemas, restaurants, clubs and a theatre.
The Philippines is currently battling Islamic State militants in the south of the country.
Islamic State flags have been spotted around Marawi and images have been circulated of smiling fighters dressed in the black clothing and posing with stolen government weapons and armoured vehicles hit by rocket-propelled grenades.