At least eight people, three of them children, are thought to have died after two planes collided mid-flight and crashed into a lake in the US state of Idaho.

The aircraft, a de Havilland DHC-2 and a Cessna TU206G, a floatplane that operates scenic flights over Lake Coeur d’Alene, collided on Sunday afternoon (local time).

The planes were carrying seven passengers, including three children, and a pilot and officers are still scouring the lake for bodies.

The lake was busy with boaters for America’s July 4 holiday weekend, and numerous personal boats immediately helped search for survivors.

Two bodies were recovered from the water, and a third was found at the bottom of the lake, the sheriff’s office said.

While the remaining victims have not been traced, they are believed to be dead.

A sonar team has found the wreckage of the downed planes in 38 metres of water. Recovering the debris from the collisions is expected to take at least a day.

Investigators are yet to determine the reason behind the mid-air collision.

Carissa Lehmkuhl was boating on the lake when the accident happened.

‘Two of my friends in the boat screamed bloody murder,” she told local news outlet KXLY.

“I saw the rest of the explosion and all the debris falling down.

“Us and kinda another boat were like the first ones at the wreckage and spotted two bodies pretty fast,” she said. “Two of the guys in our boat jumped out and, yeah, held the bodies from floating away.”

David Kilmer, whose house overlooks the lake, said he saw the aftermath of the crash.

“My wife, Rebecca, saw a fireball and wings flying out of the fireball,” he told the Coeur d’Alene Press.

“She said: ‘I just saw a plane explode’, so we went to the scene.”

Mr Kilmer said 20-30 boaters also raced to assist.

“It was a great response by recreational boaters,” he said.

“There were so many people on the lake doing whatever they could to help recover what they could. There was nothing left of the plane that was floating.”

Kootenai County sheriff’s office said there were not believed to be any survivors.

“We’re working on sonar and dive operations as we speak, but at this point, we’ve gone to a rescue – from a rescue to a recovery mode,” spokesman Lieutenant Ryan Higgins said.