Update (3:50 p.m. Pacific): the gunman is confirmed dead. One hostage, a male, is confirmed dead. A female hostage had been taped up, but left the scene relatively uninjured. The crisis is over, but the fallout remains to be seen.
Update (3:20 p.m. Pacific time): KHOU.com is reporting two people at JSC are dead.
I'm not sure if one of them is the gunman is not. The gunman is one of the dead.
5-9 shots have been reported fired, but no injuries. Most people have been evacuated from the building (Bldg 44) and are OK. There is an unconfirmed rumor that one person is being held hostage, but again that is unconfirmed. There is an intermediate school nearby that was in lockdown but that has been lifted and parents are getting their kids. Police are there, and so is a SWAT team.
MSNBC is reporting that a person with a weapon may be holed up in an office at Johnson Space Center, where NASA controls manned spaceflight missions. I have no other news at this time, but when I get it I will update here and on my Twitter page.
Thanks to Keith Irish for the heads up.