All five people aboard a single-engine airplane were killed when it crashed on Sunday in a field adjacent to a runway at a northern Colorado airport, authorities said.

Peter Knudson, spokesman for the National Transportation Safety Board, said the Piper PA-46 aircraft went down shortly before noon near the Erie Municipal Airport, about 25 miles northwest of Denver.

"We don't know yet know if it was taking off or landing," said Knudson, adding that five people were on board the plane, which crashed in clear weather.

Roger Rademacher, assistant fire chief with Mountain View Fire Rescue, said emergency crews found two people dead inside the wreckage of the six-seat airplane when they arrived at the scene.

Two people who had survived the crash and were transported to hospitals later died, Rademacher said. One had been moved by ground ambulance to a nearby hospital and the other survivor had been airlifted to a Denver hospital.

The names of the dead have not been released.

Knudson said investigators with the NTSB and the Federal Aviation Administration were at the site of the crash to try to determine its cause.