AURORA, Colo. (KDVR) – Early Saturday morning at roughly 10 a.m., an explosion happened in Aurora injuring three people and leaving roughly 400 residents without shelter.

First responders with Aurora Fire Rescue were called to a multi-family residential structure located at 14565 East Alameda after witnesses reported seeing smoke coming from a building.

Once AFR crews arrived, they began searching for the source of the smoke and that’s when the explosion happened.

Multi-family structure explosion in Aurora – debris – (Aurora Fire Rescue)

“At this time it is unknown what the exact origin of the explosion was but all searches have been negative and all crews have mitigated hazards and are out of the structure at this time awaiting assistance with utilities control,” AFR said in a tweet.

Two “green patients” were transported to University hospital and a third was taken to the Medical Center of Aurora. The extent of the third patient’s injuries is not known at this time.

According to AFR, between 300 and 400 residents who lived in the building will now be relocated to a nearby shelter until long-term accommodations can be decided upon with the help of the American Red Cross.

The ARC is now working alongside AFR to help those who have been temporarily displaced by this explosion. Volunteers have set up an evacuation center for all those impacted by this explosion at 1300 South Sable Blvd.

Residents described the explosion to FOX31 on Saturday. Read more here.