NELSON school teacher John Jackson set out on an expedition to scale the world's highest unclimbed mountain.

The 33-year-old and his 38-year-old brother Ron Jackson, of Burnley, were to climb the 28,156ft Himalaynan Kanchenjunga with Everest climber Charles Evans.

John's wife and two-year-old son were due to accompany the team on the trek as far as India where they would wait for their return.