Image copyright PA Media

Sir David Attenborough has signed up to Instagram for the first time to help spread his environmental message.

"I am making this move... because, as we all know, the world is in trouble," he said in his first video message on the social media platform.

"Continents are on fire. Glaciers are melting. Coral reefs are dying... The list goes on and on," he continued.

Within an hour of his first post, he had more than 200,000 followers, and by 16:15 BST he had 1.2m followers.

"Saving our planet is now a communications challenge," the veteran broadcaster said.

Tennis player Sir Andy Murray and body coach Joe Wicks were among those to post welcome messages.

Sir David said he would use the platform to share videos explaining "what the problems are and how we can deal with them".

Concluding his message, the 94-year-old invited viewers to "join me - or as we used to say in those early days of radio, stay tuned."

Frequent collaborators Jonnie Hughes and Colin Butfield will help manage the account and its various technical aspects.

"Social media isn't David's usual habitat," they wrote in a message accompanying the naturalist's introductory video.

Sir David's Instagram debut precedes the release of latest book and Netflix documentary, both titled A Life On Our Planet.

The film sees him reflect on his career and the decline of the planet's environment and biodiversity he has observed first-hand.