A man threatening to commit suicide with a shotgun outside United Nations headquarters surrendered to police Thursday afternoon.

The still-unidentified 44-year-old man is a Florida resident who checked into the Millennium Hotel Broadway Times Square, about a mile from the UN, on Wednesday, NYPD officials said at a news conference.

At about 10:30 am, police vehicles started to arrive and blocked the streets outside the building around East 42nd Street and First Avenue. Heavily armed police were also inside the UN building.

A man wearing a red long-sleeve shirt and blue jeans was holding a shotgun walking back and forth outside the United Nations building. He was pointing the gun at his chin.

The UN Security announced a lockdown inside UN headquarters because of ongoing police activity and all personnel and delegates at the headquarters were requested to shelter in place.

UN Secretary-General Antonio Guterres was inside headquarters at the time and brought to a secure location, according to a UN spokesperson.

After an almost three-hour standoff with police, the gunman took out a pile of documents in a red-covered envelope from his bag and handed it to police. The police then delivered it to UN staff inside the entrance, which was guarded by heavily armed police.

He dropped the shotgun and surrendered to police at about 1:40 pm, soon after his documents were delivered.

The New York Daily News reported that the documents were his manifesto about the environment.

The gunman was handcuffed and was taken into custody by the NYPD, the UN spokesperson confirmed.