"On arrival responders determined 2 planes had crashed and confirmed 3 fatalities. The public is asked to avoid the area," the agency said on Twitter, Sputnik reported.
The National Transportation Safety Board added that the crashed aircraft were Cessna 172 and Sonex Xenos.
Names of those who died have not been released, pending notification of family, CBS Colorado reported, citing the local police.
The accident is being investigated by the local police and federal aviation services.
ZZ/PR