Firefighters in the Denver metro area responded to the second large fire at an Aurora construction site in three days on Saturday. Officials have not yet determined the cause for either fire and have not suggested that they were related, but both are under investigation.

Saturday’s five-alarm fire was reported about 12.48 pm, said Aurora Fire Rescue spokesperson Andrew Logan, at a large apartment building that was still under construction. Responding crews went to the top floor of the five-story building where the blaze was reported to have started, but the dangerous conditions soon forced crews from several different agencies to focus on fighting the flames from outside the structure.