Thousands start Dartmoor's Ten Tors challenge Published duration 9 May 2015

image copyright Corporal Daniel Wiepen/Army image caption The first teams are expected to cross the finish line on Sunday

Almost 2,500 teenagers are taking part in the famous Ten Tors challenge on Dartmoor.

Competitors aged between 14 and 19 are hiking distances of up to 55 miles (89km) visiting 10 nominated tors over two days.

They left Okehampton Camp at 07:00 BST, with the first teams expected to cross the finish line on Sunday morning.

Most of the teams are from schools and youth groups from across the South West.

'Renew friendships'

But one team which completed the challenge 40 years ago when they were at St Margaret's School, Exeter, are taking part again.

Steve Hodder, the team organiser and leader, said: "It has been a big ask for many of us, but I've been really impressed by the level of commitment and determination among the group and we have been able to renew friendships and create strong bonds."

The challenge is organised by the Army and assisted by the Royal Navy, the Royal Air Force and the Dartmoor Rescue Group.

Each team has a GPS tracker, so safety teams can find out where each group of teenagers is. The tracker also has an emergency button if help is needed.

image copyright Corporal Daniel Wiepen/Army image caption The canons mark the start of the challenge at Okehampton Camp

image copyright Corporal Daniel Wiepen/Army image caption Teams left the camp at 07:00 BST

image copyright Corporal Daniel Wiepen/Army image caption Competitors will visit 10 nominated tors over the two-day challenge

image copyright Corporal Daniel Wiepen/Army image caption Teenagers from across the South West are taking part

image caption The event is co-ordinated from the Ten Tors operation room