Four people are dead and two left injured in two separate aviation incidents in Wisconsin on Saturday, officials said.

A helicopter and gyrocopter collided mid-air during an aviation convention at a Wisconsin airport on Saturday, officials said.

The incident occurred shortly before 12:30 p.m. local time in Oshkosh, according to the National Transportation Safety Board, which is the lead agency investigating the crash.

A Rotorway 162F helicopter and an ELA Eclipse 10 gyrocopter collided mid-air at Wittman Regional Airport, the Federal Aviation Administration said. Two people were on board each aircraft, according to the agency.

Two people died in the crash and two others were injured and are in stable condition, according to the Experimental Aircraft Association (EAA).

The Experimental Aircraft Association is currently holding EAA AirVenture, its annual convention and air show, at Wittman Regional Airport.

The FAA said the two aircraft were flying in the AirVenture ultralight area at the airport when the collision occurred. The crash did not occur during the air show, the NTSB said.

"These were aircraft that belonged to event attendees and were not involved in the air show," EAA said in a statement.

EAA said the "mid-air accident" occurred at the south end of the EAA AirVenture flight line at the airport and that EAA, Winnebago County Sheriff's Department and Oshkosh Fire Department personnel responded to the scene.

In the other incident, a small aircraft crashed into Lake Winnebago, killing two people, authorities said.

A single-engine North American T-6 crashed into the lake around 9 a.m. local time after just departing Wittman Regional Airport, the FAA said.

The Winnebago County Sheriff's Office said it received multiple 911 calls about the crash and several agencies, including Winnebago County Marine Units with dive rescue and recovery team members, and the U.S. Coast Guard responded to the scene.

The plane was "reportedly maneuvering before rapidly descending" from about 3,000 feet altitude, the U.S. Coast Guard Great Lakes said.

The U.S. Coast Guard recovered the bodies of the two people killed in the crash, the EAA said Sunday.

Divers were able to locate the two occupants who were aboard the aircraft, according to the U.S. Coast Guard Great Lakes.

The crash did not occur during the EAA AirVenture air show, the NTSB said.

Officials have not released the names of those killed in both accidents because their family members have to be notified, the EAA said.

ABC News' Peter Charalambous, Jessica Gorman and Teddy Grant contributed to this report.

This is a developing story. Please check back for updates.