Firefighters have removed a victim from the rubble and are still battling a blaze at the building.
Xcel spokesman Mark Stutz says the company services the natural gas meter outside the apartment building, and workers are on site to help the fire department investigate the cause of the explosion. In the meantime, Xcel has cut gas to the surrounding area.
Stutz didn't know when Xcel had last been at the site to inspect its lines but says such inspections happen "fairly routinely." Natural gas explosions are most often caused by leaking appliances.
We'll update this story as we learn more.