Relatives of those killed in the Royal Navy's worst wartime accident are among those marking its centenary.

It is 100 years since HMS Vanguard exploded and sank off Orkney with the loss of 843 lives on July 9, 1917.

Commemorations in the islands this weekend will be attended by 40 descendants of the men who died.

A wreath was laid over the wreck of HMS Vanguard in the Scapa Flow on Sunday morning, followed by a service on Hoy.

Forty-one of the warship's crew are buried at the Lyness Royal Navy Cemetery on the island.

The events culminate with a special service at St Magnus Cathedral in Kirkwall. It is due to begin at 11pm, making the moment when the ship was destroyed.

A White Ensign flag recovered from the wreck by Royal Navy divers will be presented to the people of Orkney during the service.

They worked alongside a team of volunteers to survey the wreck and replace the flag, laid by the Royal Navy in 2009, with a new White Ensign.

Naval regional commander for Scotland and Northern Ireland, captain Chris Smith, said: "The history of the Royal Navy and Scapa Flow are tightly entwined.

"Last year, we recognised the huge sacrifice made by our sailors at the Battle of Jutland and commemorated the loss of HMS Hampshire.

"Next month we will recognise the achievement of Squadron Commander Edwin Dunning with his first-ever landing of an aircraft on a ship at sea and his subsequent death a few days later, but this weekend we are firmly committed to commemorating the tragedy that was the loss of HMS Vanguard.

"The devastating explosion, completely accidental rather than a result of enemy action, was a shock when it happened and the tragic loss of more than 840 lives is still felt through their descendants and those in Orkney who feel passionately that we should mark the centenary in appropriate fashion."