PHILLIPS, Wis. -- A small airplane en route to Winnipeg that went down in northern Wisconsin fell apart in the air, killing the six people on board, a spokesman for the National Transportation Safety Board said Monday.

The Cessna 421 that crashed at 3:21 a.m. Saturday left from Waukegan, Illinois, NTSB spokesman Eric Weiss said.

"The debris field suggested an in-flight break up," Weiss said.

Lt. Gabe Lind at the Price County Sheriff's Office said the debris field from the crash stretched about 400 metres from a heavily wooded area onto a state highway.

The six people killed were identified Monday as 70-year-old Kevin James King, 56-year-old Thomas DeMauro, 21-year-old Kyle DeMauro, 63-year-old James Francis, 69-year-old Charles Tomlitz, and 45-year-old George Tomlitz. The sheriff's office has said they were headed to Canada for a fishing trip.

The DeMauros and King are from Bensenville, Illinois. Francis is from Norco, California. Charles Tomlitz is from Addison, Illinois, and George Tomlitz is from Brookfield, Illinois. Authorities did not say how they knew each other or how they were related.

NTSB investigators say there was a discussion between the pilot of the plane and air traffic controllers about "local weather phenomenon" in Catawba, Wisconsin, which is near the crash site just southwest of the city of Phillips. Soon after, the aircraft dropped off radar.

Weiss said investigators are still trying to determine what type of weather the plane encountered and whether it caused the crash.

Thomas DeMauro was a physical education teacher at Tioga Elementary School in Bensenville, Illinois, and Charles Tomlitz was a maintenance director for the district, according to a Facebook post from the school.

"Mr. DeMauro and Mr. Tomlitz will be missed by all the Tioga Community," the school's co-principals wrote in the post on the Tioga Elementary School Facebook page.

In a statement to WSAW-TV, the DeMauro family expressed gratitude for the outpouring of support.

"We would also like to express our heartfelt condolences to the other families affected by this tragedy. Tom was our beloved son, husband, father, brother, uncle, friend, teacher and coach," the statement said. "Kyle was our dear son, brother, grandson, nephew and friend; a compassionate young man who had a promising future."