A Planet Earth II camera crew was 'emotionally devastated' after they witnessed 150,000 antelope drop dead in just three days, a producer revealed.

The team was filming the Saiga antelope in a remote region of Kazakhstan for the upcoming 'grasslands' episode, which follows the animals of the world's plains.

After days of searching, the crew tracked down a calving herd and watched as thousands of antelopes gave birth to their calves together.

Natural wonder: The Planet Earth II crew was filming the Saiga antelope (seen above in a file image taken in Russia) in a remote region of Kazakhstan for the upcoming 'grasslands' episode

Devastated: As thousands of females gathered to give birth at the same time, a disease swept across the herd and killed some 150,000 in three days. File image of dead Saiga antelope

However at the same time, a disease swept across the herd and killed some 150,000 in three days, the Daily Mirror reported.

Producer Chadden Hunter told the newspaper: 'At the time we thought we were watching the greatest natural catastrophe that I’d ever heard of.

'We watched 150,000 of these magnificent animals die in front of us.

'At the time we didn’t know if it was the final extinction of the species, which was devastating, emotionally, for the crew.'

Deadly disease: File image showing a herd of dead Saiga antelope struck by the same disease

The episode, which airs this Sunday night, also features dramatic footage of a Cape buffalo facing off against a pride of lions.

In another scene, viewers will see how intelligent bee-eater birds use herds of elephants to help them find their next meal.

Planet Earth II: Grasslands is on BBC1 at 8pm on Sunday