This Mayo Clinic medical helicopter was inadvertently started by a child Saturday at an air show in Mankato. This is a file photo. (Dennis McGrath/The Minnesota Star Tribune)

A boy about 6 years old climbed into a Mayo Clinic helicopter at an air show near Mankato and fired up the engine, setting off a tense scene on the tarmac until a worker removed the child and shut off the chopper, a witness said Monday.

The incident occurred Saturday afternoon on the first day of the Minnesota Air Spectacular at the Mankato Regional Airport.

The whirring rotor blades knocked over a large sun shield on the tarmac, and two people were hit and slightly injured by the fabric-like screen, according to a statement released by Mayo.

The helicopter is operated by Mayo Clinic Medical Transport and is based at the Mankato airport for emergency runs in a 150-mile radius.

A member of Mayo's aviation team shut down the helicopter, according to a statement issued by the clinic.

Agro Gushwa, a ticket taker at the show, said, "This kid started it up, and the propeller started spinning." Gushwa, 15, began video-recording the scene with his cellphone.

"The door was open … and he just walked in," he said.

Gushwa said the Mayo staff member "ran over and got [the boy] out" after about a minute. It took another 90 seconds or so for the staff member to shut down the helicopter, Gushwa added.

Once out of the chopper, the boy "ran to his father, who gave him a hug and told him it was OK. It was fine."

Gushwa, who estimated the boy's age as about 6, said the child "was crying really bad."

A spokesman for Mayo Clinic Medical Transport declined to field questions Monday about the circumstances surrounding how the boy started the Eurocopter EC145, a twin-engine light utility helicopter that can be configured to carry up to nine passengers and two crew members. Spokesman Glen Lyden said the boy was alone in the cockpit, but he did not know whether anyone else was farther back in the aircraft.

Another show attendee, Terry Thompson, of Waconia, said he was walking by the helicopter as the rotors on the top and on the tail were spinning.

"I kind of froze for a second and thought, 'Now, do I run up in there?' " he said.

Air show Director Mark Knoff said the "unfortunate incident" was reported to an on-site Federal Aviation Administration official.

Knoff, himself a helicopter pilot, said choppers are started in various ways and he's unaware of how the boy got the engine cranked up.

FAA spokeswoman Elizabeth Isham Cory said agency "investigators attend all air shows in order to oversee the event and were on scene at the time."

The investigation into the incident is now being led by the National Transportation Safety Board, Isham Cory said. However, NTSB spokesman Keith Holloway said this "doesn't appear to be something that [the agency] would investigate" because there was no crash and no injuries onboard.

The aircraft has been removed from service for inspection and maintenance, which is routine, Mayo's statement said.

Mayo said it is conducting its own investigation.

Along with basing a helicopter at the Mankato airport, Mayo Clinic also has emergency helicopters at its headquarters in Rochester and at the Chippewa Valley Regional Airport in Eau Claire, Wis.

Paul Walsh • 612-673-4482