An exchange of gunshots between Marines serving as Senate security and ''perceived NBI (National Bureau of Investigation) agents'' took place in the second floor of the Upper Chamber on Wednesday night.

Senate Secretary Mark Lleandro Mendoza told reporters that the ''perceived NBI'' fired first and Senate security retaliated. It was not known if there were injuries.

Senate President Alan Peter Cayetano said they were having a caucus when they received reports that armed men entered the building from the side of the Government Service Insurance System (GSIS). ''Gunshots were exchanged. The NBI are denying these are their men. We don't know what is happening. Everyone is locked in their rooms now,'' he said.

'' NBI, what is happening? PNP (Philippine National Police), what is happening?,'' added Cayetano in his Facebook page.

NBI Director Melvin Matibag told Frontline Philippines that he did not send any agents to the Senate.

Cayetano said they just received the articles of impeachment from the House and they were discussing how to tackle it when gunshots were heard.

The Senate was placed under lockdown. It was lifted to allow Interior Secretary Jonvic Remulla and Major Gen. Anthony Aberin, Metro Manila's police chief, to enter.

Remulla said he came in to make sure every one is safe, including Senator Ronald Dela Rosa, who has an arrest warrant from the International Criminal Court. He said he will not arrest Dela Rosa. PHS