Two small planes have collided in the air in the US, leaving one aircraft nearly ripped in half and forcing the pilot of the other to deploy a parachute.

Both planes landed safely and no-one was injured, officials said.

The aircraft were getting ready to land at a small regional airport in a suburb of Denver, Colorado, on Wednesday when they collided, according to the National Transportation Safety Board and South Metro Fire Rescue.

“Every one of these pilots needs to go buy a lottery ticket right now,” Arapahoe County Sheriff’s Deputy John Bartmann said.

“I don’t remember anything like this – especially everybody walking away. I mean that’s the amazing part of this.”

June Cvelbar told the KUSA TV station that she witnessed the collision while walking in Cherry Creek State Park.

“I saw two planes in the sky. I saw a larger green plane, which I thought was a tow plane, along with what I thought was a glider being towed by it. I heard a noise but didn’t realise that the two planes had collided,” she told KUSA.

Ms Cvelbar said she saw the green plane fly off and shortly after saw the smaller plane deploy its parachute.

She said she initially thought it was a training exercise.

“When I realised that the small plane was going down I ran toward it. The pilot and his passenger were up and about,” Ms Cvelbar said.

A Key Lime Air Metroliner that landed safely at Centennial Airport after a mid-air collision near Denver
A Key Lime Air Metroliner that landed safely at Centennial Airport after a mid-air collision near Denver (CBS Denver via AP)

The pilot was the only person aboard a twin-engine Fairchild Metroliner that landed at Centennial Airport despite suffering major damage to its tail section.

The plane is owned by a Colorado-based company, Key Lime Air, that operates cargo aircraft.

A pilot and one passenger were on the other plane, a single-engine Cirrus SR22, which unleashed a red and white parachute and drifted down to a safe landing in a field near homes in Cherry Creek State Park, Mr Bartmann said.

It was not immediately known who owned the Cirrus, he said.

The National Transportation Safety Board tweeted that it was sending staff to investigate.

Key Lime Air will co-operate with the investigation, the company said in a statement.