Four people are dead and two are injured after two aircraft collided in midair and another crashed into a lake Saturday shortly before an air show at a major aviation convention in Oshkosh, Wisconsin, authorities said.

Two people died when a North American T-6, a vintage military training craft, crashed around 9 a.m. into Lake Winnebago, according to the Coast Guard, who recovered the bodies of the two people on board Saturday night.

The plane descended rapidly from an altitude of around 3,000 feet, the Coast Guard said. Several agencies, including the Oshkosh Fire Department and the Coast Guard responded to the crash, according to a statement from the Experimental Aircraft Association, which organizes the annual AirVenture convention.

Two people were killed in a separate crash Saturday around noon, when a RotorWay 162F helicopter and an ELA 10 Eclipse gyrocopter collided midair. The accident happened in an area of Wittman Regional Airport designated for the event, organizers said.

Gyrocopters look like small helicopters, but their propellers spin naturally, without the help of an engine.

Two people who were injured in the accident were transported to a local hospital and are in stable condition, the statement said.

It is unclear which victims were on which aircraft, but event organizers said the helicopter and gyrocopter belonged to event attendees and were not involved in the air show.

Authorities have not released the names of people who died in either accident, pending notification of relatives.

The airshow began around 2:45 p.m. after a short delay, organizers said.

The AirVenture convention is a multiday event, featuring air shows, fly-in campgrounds and fireworks. It boasts "the highest concentration of aircraft in the world."

Organizers published guidelines from the Federal Aviation Administration for participants planning to fly an aircraft into the festival. The National Transportation Safety Board said it is sending an investigator to begin determining the causes of both accidents.