A plane carrying six members of a University of Michigan organ transplant team went down Monday afternoon in Lake Michigan shortly after the pilot signaled an emergency, authorities said. There was no word on survivors.

As many as 32 divers from the police, fire and sheriff's department were searching near debris and an oil slick in about 20 feet of water, Milwaukee Fire Chief Doug Holton said.

Federal Aviation Administration spokesman Tony Molinaro said the Cessna Citation took off from General Mitchell International Airport in Milwaukee at 4 p.m. and was headed for Willow Run Airport near Detroit, a 42-minute flight.

"Within five minutes of its departure from the airport the pilot declared an emergency and requested a return to Mitchell but at that time the plane was no longer on our radar screens, so we've contacted the Coast Guard to begin a search and rescue mission," Molinaro said.

The six people aboard included two crew members, he said.

Witnesses saw the plane go down about six minutes after takeoff, according to U.S. Coast Guard Capt. Bruce Jones.

Molinaro said they found aircraft debris about six miles northeast of Milwaukee, but have not found any of the passengers.

The plane was leased by the University of Michigan Survival Flight air ambulance program, the University of Michigan Health System in Ann Arbor said in a statement. It was owned by Southfield, Mich.-based Toy Air Inc. and based at Willow Run, near Ypsilanti.

The University of Michigan Survival Flight team included two members of the staff of Marlin Air, which flies all Survival Flight airplane missions, and four University of Michigan employees.

The university said the team returning from Milwaukee with unspecified organs for transplant to a patient in Michigan included:

— Dr. David Ashburn, a fellow in pediatric cardiothoracic surgery.

— Richard Chenault II, a transplant donation specialist with the university transplant program.

— Richard Lapensee, a transplant donation specialist with the university transplant program.

— Dennis Hoyes, a Marlin air pilot.

— Bill Serra, a Marlin air pilot.

— Dr. Martinus "Martin" Spoor, a cardiac surgeon who had been on the faculty since 2003.

"The thoughts of the entire university community are with the families of those involved this evening, and we take consolation in the fact that the team was on a mission to help another," said Dr. Darrell A. Campbell, chief of staff of the University of Michigan Hospitals & Health Centers.

When system officials found out about the crash, they notified a transplant team in Michigan to stop preparing the transplant candidate. The patient was in critical condition, the university said.

The university wouldn't release any information on the patient, citing confidentiality.

Lapensee's mother-in-law, Sharon Manier, said Monday evening that the family was asking for privacy.

"We've gotten no word," Manier said from Lapensee's home in Belleville.

Jay Campbell, executive director of the Wisconsin Donor Network, declined to say which area hospital they were working with, citing privacy regulations.

Jones said the water temperature is 57 degrees and survivors could live for 16 hours. He said they have not found any bodies.

"Our primary focus is on finding any survivors there may be from this incident," he said.

Holton said they would dive until it got dark and then resume again Tuesday morning.

He estimated the plane was going 185 to 190 mph. The impact on the water would be "absolutely devastating", Holton said.

They have recovered debris and planned to bring it in to be looked at, Jones said.

At around 4 p.m. light rain was falling at the airport with winds at 12 mph, gusting to 22 mph, according to J.J. Wood, meteorologist the National Weather Service.

Jerry Guyer, a salvage and diving guide, used his high-definition sonar unit to help in the search. He said the unit is towed in back of his boat by a 50-foot cable and can detect objects within 100 feet of it.

"I used to look for shipwrecks and it works very well for anything on the bottom, from a car tire up as far as being able to pinpoint an item and location," he said.

Milwaukee airport spokeswoman Pat Rowe said the airport was closed for about 20 minutes after they didn't hear back from the plane in case it returned.

Bob Bruner of Mequon was a passenger on a Northwest Airlines flight landing in Milwaukee around the time of the crash.

"They diverted us and they told us there was an emergency (at the airport)," Bruner of Mequon told WISN-TV in Milwaukee.

Bruner said that the pilots onboard their flight told passengers that the runways needed to be clear, and they circled the airport several times before landing.