A number of heavily armed men garbed in black and wearing face masks opened fire at guests at Resorts World Manila, a resort located near an international airport in Pasay City, Philippines.

Explosions were heard in the building at around midnight on Thursday local time. A still unknown number of guests and security forces were reported wounded, local media Interaksyon reported.

ISIS has claimed responsibility for the attack, saying some "lonewolf soldiers" carried it out, according to the SITE Intelligence Group.   

Witnesses said the suspected terrorists accessed the casino area through a restaurant located at the south side of the hotel. An elevator from the parking area goes directly to the second, third and sixth floors of the building.

The attacks were carried out mostly on the second and third floors.

A hotel supervisor, Jun Mangosing, said he saw armed men "combing through the third floor," where VIP casino rooms frequented by foreign clients, including Korean, Japanese and Chinese players, could be found, Interaksyon reported.

The attackers reportedly poured flammable liquid on casino tables on the second floor and set them on fire, a witness told ABS-CBN News.

The casino employee said that in the middle of the chaos, some guests fled through the emergency exits while others hid in the basement where the employees' locker rooms were.

The police and SWAT teams are now on the scene.

The resort was put on lockdown following the attack.

"Operations of the Philippine National Police are currently ongoing to address the situation," Resorts World Manila posted on Facebook. "We cannot share with you any details that may jeopardize their movement at this point. We have no official information as to the identity or affiliation of the persons responsible for this attack."

"The Company has followed emergency protocols to ensure safety of guests and employees as far as the situation allowed. We will update you at the appropriate time. Again, we ask for your prayers and consideration during these trying times."

Stephen Reilly, the resort's Chief Operating Officer, said the situation is under investigation.

"We are still investigating the situation," Reilly said in a statement. "We are searching the area as much as we can to make sure the building is clear."

Resorts World Manila is an integrated resort complex that houses a number of hotels, bars and restaurants. The casinos serve as a major tourist attraction.  

The Philippines is still grappling with terrorist attack in Marawi City, located in the southern Philippine island of Mindanao, which began last week when an ISIS-linked terrorist group called Maute torched several buildings and took hundreds of hostages, including church workers and a parish priest.

The Maute fighters reportedly killed Christians who attempted to escape the city. Some Muslim residents helped Christians hide and flee to safer locations.

The fighting continues in Marawi, and reports claim the terrorists are slipping into the neighboring city of  Iligan disguised as refugees. Philippines president Rodrigo Duterte declared martial law over the entire island of Mindanao.