A NASA spokesman says the building at the center of a security scare at Houston's Johnson Space Center is one of the smaller structures on the space center campus, where Mission Control is based.
The building has been evacuated following reports of a gunman inside. News reports say the building houses communications equipment and a tracking development laboratory.
The NASA spokesman declined to speculate on how an armed person might have slipped past NASA security. There's no word yet on the identity of the armed man.
Johnson Space Center security officers and Houston police, including a SWAT team, are on the scene.