A pilot and two passengers have died when a light aircraft crashed just north of Mount Gambier in South Australia's south-east.

The victims were 78-year-old Adelaide Hills man, Grant Gilbert, who was piloting the aircraft, and a 43-year-old woman and a 16-year-old girl, both from Mount Gambier.

Mr Gilbert became the licence holder and operator of the 25-year-old single-engined plane in early 2014, and flew it mainly between Adelaide, Mount Gambier, Port Lincoln and Murray Bridge, according to aviation records.

State MP Michael Pengilly said he was saddened his good friend Mr Gilbert was killed, and for the tragic loss of the two female victims.

"Grant and I go back 20 years, when he was my deputy chair of the regional health board and our friendship continued over the years," he said.

"He was a tireless community man and a very good businessman. A true and loyal husband and father."

Plane extensively damaged on impact

The plane crashed into a paddock in Suttontown, just south-west of Mount Gambier's airport, just before 10:30am.

There were no survivors from the crash and the local fire service said the plane was extensively damaged.

But Detective Superintendent Grant Moyle told reporters "there was no actual fire as such".

Investigators check the severely damaged nose of the aircraft. ( ABC News )

He said the aircraft took off from the nearby airport a little after 10:00am and the first report of a crash came at 10:24am.

Investigators brought in lights to help their probe of the accident site. ( ABC News: Chris McLoughlin )

There was thick fog in the south-east during the morning, which delayed some local air traffic.

"This morning in Mount Gambier it was foggy, and cold and wet," Detective Superintendent Moyle said.

Four Australian Transport Safety Bureau (ATSB) investigators have travelled to Mount Gambier to help local investigators.

"The team will be examining the site and wreckage, gathering any recorded data and interviewing any witnesses," the ATSB said in a statement.

The ATSB said the plane involved was a TB10 Tobago.

Detective Superintendent Moyle was unable to give details about the nature of the flight.

"I understand some next of kin certainly have been advised," he said.

"I won't comment on its course or mission at this point."