Stephen Hawking has warned aliens could kill humans if we ever try to contact them as he spoke out about his fears that alien life could conquer Earth.

The world’s most famous theoretical physicist warned humans to be hesitant about making contact with our extraterrestrial neighbours.

He said while planet Gliese 832c - a hot super-Earth discovered earlier this year - has the potential to support alien life, it is unlikely that any life out there would be pleased to hear from us.

In a documentary entitled ‘Stephen Hawking’s Favourite Places’ , he said: “One day, we might receive a signal from a planet like this, but we should be wary of answering back.

“Meeting an advanced civilisation could be like Native Americans encountering Columbus. That didn’t turn out so well.”

He went on to say that alien life could be "rapacious marauders roaming the cosmos in search of resources to plunder, and planets to conquer and colonise”.

This is not the first time Professor Hawking has spoken about his fears, having aired his concerns on the Discovery Channel back in 2010.

The scientist claims that as he gets older, he becomes more convinced that humans are not alone, adding: “After a lifetime of wondering, I am helping to lead a new global effort to find out.”

Planet 832c has five times the mass of the earth, and sustains a similar temperature.

Described as an inhabitable super-earth, it is 16 light-years from our planet.

The prospect of an alien invasion is not the only thing Professor Hawking is worried about.

He has also warned planet Earth faces becoming as hot as Venus, if climate change is not controlled.

Speaking to the BBC, he said climate change could turn the planet into a hothouse, adding President Trump’s decision to pull out of the Paris Climate agreement could accelerate the threat.

He said: “We are close to the tipping point, where global warming becomes irreversible.

“Trump’s action could push the earth over the brink, to become like Venus, with a temperature of 250C, and raining sulphuric acid.”

Expanding on his fears, he said humans may one day have to consider living on a different planet if climate change ravages our own world.

According to reports in Live Science, however, experts do not believe Earth could hit those extreme temperatures, because it is further away from the sun than Venus and does not have a carbon dioxide atmosphere as thick as Venus.

Pennsylvania State University climate scientist Michael Man said: “Hawking is taking some rhetorical license here.

“Earth is further away form the sun than Venus and likely cannot experience a runaway greenhouse effect in the same sense as Venus — i.e. a literal boiling away of the oceans.

“However Hawking’s larger point — that we could render the planet largely inhabitable for human civilisation if we do not act to avert dangerous climate change — is certainly valid.”