Nine people have died after their plane crashed during a skydiving trip near Umea, a small university city in northern Sweden, authorities have said.

The small plane designed to carry parachutists crashed on an island on the Ume river shortly after taking off, police spokesman Peder Jonsson said, adding the cause for the incident was unknown. 

He said those on board were on a skydiving trip.

The region's main University Hospital of Umea confirmed there were no survivors and relatives of the deceased had been notified.

The plane, a Gipps Aero GA8 Airvan, had taken off from Umea airport.

Amateur footage posted online by the Swedish daily Afton bladet shows the plane plunging from the sky in a vertical line.

"I heard a weird sound, which didn't sound normal," one witness, Peter Larsson, told the daily newspaper Dagens Nyheter. "I looked up and saw a plane spinning like a top.

"At first I thought it was an acrobatic flight but we quickly realised that something was wrong."

Neither Mr Jonsson nor the hospital immediately identified the victims' names or nationalities.