When the crew saw the snakes for the first time, they were too shocked to film - and host Sir David Attenborough had never seen anything like it either, it was claimed.
Among the millions of viewers captivated by the footage shown at 8pm last night was Olympic rower Will Satch, who described it as a "real life horror film".
He tweeted: "Bloody snakes chasing those poor sea swimming iguanas. David Attenborough is exactly what this world needs and plenty of him."
Sir David's commentary told how the snakes' eyes are poor, but they can detect movement and are on alert for other iguanas after seeing one.
Viewer Alex Barreto praised the "absolutely disgusting but incredible footage", while Claire Macmillan expected to have "nightmares about those racer snakes".
Meanwhile ITN lighting cameraman Matt Freestone hailed the sequence as "probably the most brilliantly edited piece of television I've seen in ten years".
The hotly-anticipated series, which is formed of six parts and follows on from the first Planet Earth in 2006, has taken three years of filming and 117 filming trips.
The first episode focused on island life and used nine filming locations. Next week the show will look at mountain animals including a rare sighting of snow leopards.
MailOnline TV critic Jim Shelley said: "One chase scene and narrow escape was more thrilling than anything in James Bond and actually not that different."
He added that the racer snakes "sounded scarier and scary enough without the sight of them hunting in packs, like a scene from Indiana Jones".
And Daily Mail TV critic Christopher Stevens, who gave the first episode of the new series five stars, described last night's sequence as "truly edge-of-the-seat".
He said the predators writhed together 'like a mythical animal with a dozen heads' and "they looked like animated clay monsters from an old-fashioned horror movie".
Meanwhile BBC chiefs will be celebrating today after the programme claimed a massive audience of 9.2million and a 36 per cent share of TV viewers.
This made it Britain's most watched natural history programme in more than 15 years - and it was more popular than the first series debut watched by 8.74million viewers.
And it has also been revealed that the series does not feature any penguin deaths because they look too much like humans, so it would upset viewers.
