Viewers have been left in tears after watching the first episode of Planet Earth III

Sir David Attenborough is back on the small screen as Planet Earth III premieres around the world.

It's a bittersweet moment for fans of the incredible nature documentary series.

This is the third and final instalment and while it delivers on jaw-dropping visuals, we are again reminded of the frailness of our planet.

There are eight episodes of this season and they touch on all facets of our world.

Deserts, grasslands, forests and oceans are explored and we also get to see the human impact on the natural world as well as the heroes who are trying to save everything.

The first episode, 'Coasts', aired on Sunday (October 22) and viewers were blown away by the footage.

"This emotional roller coaster on a Sunday evening... I shed tears for the mess we have made of our planet. I'm glad this beauty made it back into the ocean," one person said, referencing the part about the green turtle.

Another added: "I feel so sad for David Attenborough. He started off his career informing us about the wonders of the natural world and at an age when he shouldn’t have a care in the world he is desperately trying to get us to stop destroying the planet."

There were also some viewers who believe climate change deniers should be forced to watch the series.

One person wrote: "No matter how much people in the world deny that climate change isn't real, this programme shows us all that it is real. Governments should act now and fast."

A different user commented: "An amazing episode of #PlanetEarth3. Extraordinary that the climate change deniers go silent on social media when David Attenborough presents irrefutable evidence of the peril we face."

Sir David explains to the viewers in the first episode that 'we must now look at the world through a new lens'.

It's a very different globe than when the first Planet Earth was released, and now the stakes and challenges are much higher.

Mike Gunton, Planet Earth III’s executive producer, was 'delighted' to have Sir David narrate the show's last instalment. “As ever, he has brought his huge enthusiasm and wisdom, has been encouraging about our new perspective and has, I know, really enjoyed seeing the extraordinary new wonders brought to the screen," he said.

The next episode is titled 'Ocean' and will premiere this Sunday.