(CNN) -- Some hostages escaped a Virginia post office where a disabled man held them prisoner for more than six hours Wednesday, according to the town's mayor.
Mayor Trent Crewe said he did not know how many hostages were left in the building.
Five people -- three postal workers and two customers -- were taken hostage after a man entered the Wytheville, Virginia, post office about 2:30 p.m. and fired a shot, Crewe said.
Virginia State Police Sgt. Michael Conroy told CNN affiliate WVVA that multiple shots were fired. No one was reported hurt, Crewe said.
An unidentified witness told CNN affiliate WDBJ that he, a fellow window clerk and the postmaster were in the building when the gunman entered, but they quickly fled. He added that his supervisor was one of the hostages.
There were reports that the man has a "device," and it appears that his car, parked outside the office, is equipped with some type of device as well, Crewe said. He did not elaborate on what the device could be.
"The police authorities have told me they are acting on the assumption there is an explosive device of some kind in some location," Crewe said. "There is a bomb squad, in fact more than one bomb squad on site, but we cannot confirm any explosives."
The surrounding area of downtown Wytheville has been evacuated, Crewe said.
The gunman is in a wheelchair, but the extent of his disability is unknown, said U.S. Postal Inspection Service spokesman Peter Rendina. The suspect has asked for pizza but made no other demands, Rendina said.
The gunman's motive is still unclear, Crewe said.
Agents with the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives are also on scene, Crewe said.
"Hopefully it'll be shortly resolved in a peaceful manner," he said.
Wytheville is a small town in southwestern Virginia in the foothills of the Blue Ridge Mountains. It has a population of just over 8,000.
CNN's Shawn Nottingham contributed to this report.