[Updated at 2:19 p.m.] The Discovery Channel day care has been evacuated to a nearby area, according to CNN affiliate WJLA. The day care had about 100 kids, WJLA reported.

[Updated at 2:18 p.m.] The FBI's bomb techicians and ATF agents have been sent to the scene of the hostage situation in a Washington suburb, spokesmen from both agencies said.

[Updated at 2:17 p.m.] Renard Jenkins, who works across from the Discovery Channel headquarters where the hostage drama is unfolding, said he sees the mobilization of a bomb squad and a large armored vehicle pulling a trailer.

"Police are on high alert, positioning themselves behind columns, cars, anything that gives cover. All have their weapons drawn," Jenkins said. "From what we're seeing, everyone seems to be calm."

He said he cannot see into the lobby where the hostage-taking is apparently under way, but can see the activity immediately outside.

[Updated at 2:07 p.m.] CNN affiliate WJLA is reporting that police told them a man entered the lobby and may have fired a weapon and declared, "Nobody is going anywhere."

iReport: Are you there? Send photos, video

WJLA: Discovery headquarters evacuated

[Updated at 1:52 p.m.] A SWAT team and additional resources are responding, said Montgomery County police Cpl. Dan Friz. Authorities were trying to get in touch with the man believed to have taken a hostage.

It appears the man has some kind of explosive device on his person, Friz said. Fire marshals with explosives experience were assisting.

[Updated at 1:44 p.m.] The Discovery Channel sent an e-mail to all employees in the building at 1:21 p.m. telling them they "have reason to believe there is an armed gunman at One Discovery Place."

[Updated at 1:39 p.m.] At least one hostage is confirmed at the headquarters of the Discovery Channel in Silver Spring, Maryland, police said.

[Posted at 1:34 p.m.] A police emergency response team was responding to reports of a man with a gun and possible explosives at the headquarters of the Discovery Channel in Silver Spring, Maryland, a police spokeswoman said.

Montgomery County police received the call at about 1 p.m., said Angela Cruz. The call came from One Discovery Place, the channel's headquarters.

The area has been evacuated, Cruz said. No further information was immediately available.