The shores of remote islands, mysterious marine forests, the "inner space" of the sea's darkest depths: Blue Planet II transports audiences to new underwater realms, but also shines a light on dire, man-made problems plaguing the world's oceans — including plastics, coral bleaching and global warming.

The anticipated documentary series — produced over more than four years with the latest camera technology, across 125 expeditions and from more than 6,000 hours of underwater dive footage — returns 16 years after the original landmark production.

Click the video above for a glimpse of the series. 

The new instalments are hosted once again by esteemed naturalist and broadcaster David Attenborough. 

"There are three times more human beings on this earth than when I made my first television program," the 91-year-old, dubbed a British "national treasure" by GQ magazine last year, told CBC News at a recent premiere screening in London.

"There's much less space for wildlife, so if you're a chimpanzee or if you're an orangutan or indeed if you're a coral reef, you'd say the world is not as good as it was."

Produced by the BBC, Blue Planet II debuts in the U.K. this month and in Canada in early 2018.

With files from Thomas Daigle