Video: Terrifying moment skydivers survive mid-air plane collision

The collision sent one of the planes off fire-balling into the distance.

All the 11 people involved miraculously survived by spontaneously jumping out seconds after the crash and landing safely on the ground.

The two planes crashed at an altitude of 12,000 feet while the experienced skydivers were preparing to jump in formation over northwestern Wisconsin.

"We do this all the time," Mike Robinson, an instructor aboard one of the planes said. "We just don't know what happened for sure that caused this."

Mr Robinson, 64, said he and three other skydivers had climbed out on to a step on their Cessna 182, and were poised to jump, when the second plane came from behind and crashed down on top of theirs.

"It turned into a big flash fireball, and the wing separated," he said.

"All of us knew we had a crash. The wing over our head was gone, so we just left".

The pilot of Mr Robinson's plane landed with an emergency parachute and was treated in hospital for minor injuries. The pilot of the second plane returned to Richard I. Bong Airport and landed.

The skydivers said they were forced to steer around debris and had 'parts of the airplane floating in the air with us' as they travelled down to the ground.

Officials from the Federal Aviation Administration were on Monday investigating the cause of the accident.

A witness on the ground said he heard a 'boom and looked up and there's a fireball and smoke'.

Braydon Kurtz said one plane 'was circling down and one was going down straight'.

Mr Robinson said while everyone responded professionally and quickly, they were lucky to have been in place to jump when the collision happened.

"It might've been a lot worse," he added. "Everybody, to a person, responded just as they should, including the pilots."

A skydiving accident in Belgium last month killed 11 people when a plane went into a nosedive as part of its wing broke minutes after take-off.