After more than a five-hour standoff at Pittsburgh's Gateway Center, a man surrendered peacefully just before 2 p.m. and released his hostage.

Pittsburgh police Chief Nate Harper said the man is a 22-year-old ex-military personal who is not related to anyone in the office. WTOV9's sister station in Pittsburgh, Channel 11 News, reported that the man has been identified as Klein Michael Thaxton, of Pittsburgh.

A person inside of the building told Channel 11 that a man armed with a gun and at least two duffle bags with unknown contents is on the 16th floor. Initial reports indicated that the man said he had explosives in the bags.

Sources said the man pulled out the gun around 8:20 a.m. A security guard told Channel 11 that he overheard a female say, "Don’t come in here. You will get hurt." The guard said he then called police.

Channel 11 News reported that the office where the situation happened handles union matters and pensions.

Harper said the gunman's mother was brought into Gateway Center 3  just before 11 a.m. to possibly help with negotiations. Harper said the situation was contained to one suite.

The 16th floor was been placed on lockdown and the rest of the building was been evacuated. Bomb sniffing were sent into the building. Roads surrounding Gateway Center were shut down as police and SWAT officials investigate. The Gateway T stop was also shut down and Port Authority buses in and around the area were diverted.

Stay with NEWS9, WTOV9.com and WTOV9 Mobile for continuing coverage as details become available.