Witnesses said they saw masked gunman attacked the hotel.
Police are already in the scene. Parts of the hotel is on fire, Xinhua reported.
The Islamic State terror group has claimed responsibility. Eyewitnesses also said they heard two men running into the resort complex with guns , shouting 'ISIS' and poured a flammable substance on gaming tables.
However, the police chief stressed that there was no concrete evidence to whether it was an act of terrorism.
Meanwhile, 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 are responsible for the attack at Resorts World Manila.
Resorts World Manila is an integrated resort located in Newport City opposite the Ninoy Aquino International Airport Terminal 3 in Pasay City.
US President Donald Trump is aware of the current situation in Manila, a presidential spokesman said today.
Trump "is aware of the situation in Manila and being provided updates by his national security team", White House Press Secretary Sean Spicer said in a tweet.