Valeri Girbakin, a spokesman for Moscow police, said there were between 40 and 50 hostage-takers, among them women of "non-Slavic" nationalities.

"They are demanding to resolve the situation in the Chechen Republic, specifically pulling out Russian troops," he said.

Witnesses said a large group of armed men stormed the Palace of Culture of the Podshipnikov Zavod, fired several shots into the air and refused to let adults leave the theater.

Girbakin said there were about 600 hostages inside. Initial reports put about 40 actors, 35 musicians, 50 staff members and an audience of 600 inside the hall.

Several hundred police officers and security officials and numerous emergency vehicles were deployed around the theater. The standoff began about 9:05 p.m. (1:05 p.m. ET).

There was a brief exchange of gunfire about five hours into the standoff, but there were no reports of casualties.

Russian radio broadcast pleas from hostages speaking by cell phones who said that if police stormed the theater, the gunmen would kill 10 hostages for each hostage-taker killed by police. The gunmen also told police they have mined parts of the building.