At least a dozen gunshots rang out inside the Philippine Senate building in Manila earlier on Wednesday as police and marines moved to arrest Senator Ronald "Bato" Dela Rosa on an International Criminal Court warrant for alleged crimes against humanity linked to former President Rodrigo Duterte's brutal war on drugs, a campaign that left more than 6,000 suspected drug dealers dead in operations.

Reuters reports that it is unclear who fired the burst of shots inside the Senate building, but it occurred as Dela Rosa was taking refuge inside the building amid efforts to arrest the senator on an ICC warrant for alleged crimes against humanity.

Other media outlets captured the chaotic moments when shots rang out in the Senate building's hallway.

"About 15 shots were fired, and we were forced to pull back," Al Jazeera reporter Jamela Alindogan said, adding that security forces then ordered the evacuation of the building.

Dela Rosa posted a video on Facebook earlier, anticipating his arrest, and urged citizens to come to the Senate building to block his arrest: "I am appealing to you. I hope you can help me. Do not allow another Filipino to be brought to The Hague."

On Tuesday, Dela Rosa, a former police chief and top enforcer of former President Rodrigo Duterte's war on drugs, urged President Ferdinand Marcos Jr. not to allow the ICC to arrest him.

The ICC unsealed its arrest warrant on Monday, accusing Dela Rosa of the same crimes as Duterte, who is awaiting trial in the Netherlands.

Al Jazeera's Alindogan said that while violent incidents are not unusual in Manila, it was highly unusual for this type of chaotic event to occur in the Senate building, "where there's supposed to be some sort of civility."