There’s a set of UFO hunters who are convinced that Nasa is covering up the remains of an ancient civilisation on Mars.

In the hope of backing up their bizarre theory, they’ve spotted what they believe to be everything from military bunkers to coffins on the red planet.

Their latest ‘sighting’ of a rock by the Opportunity rover described as a ‘man-made dome’ that they say was left behind by an alien race sometime during Mars’ watery past.

They claim a glow or light in the middle of the dome is evidence that it may be metallic and reflecting sunlight.

‘The existence of domes on Mars proves that someone or something built them in the past,’ wrote conspiracy website, the Unsilent Majority.

‘Is it possible that we are looking at some sort of building left behind by ancient inhabitants on Mars?

‘What if we are looking at the ultimate evidence that proves the red planet was in fact inhabited in the distant past by beings that developed across the red planet just as humans developed across Earth?’

‘While it could be some sort of natural rock formation, that would need to be extremely strange, we cannot dismiss the fact that we could be looking at the remains of an alien structure on Mars.’

The site says there may also be a third option to explain the dome’s presence.

They say that Nasa has developed a secret space program and flotilla that operates in space.

While this seems to be the first dome found on Mars, other have been found on the surface of the moon.

These are largely though to be the result of ancient eruptions that formed flat and wide volcanoes.

The latest sighting follows a similar 'discovery' earlier this year in which conspiracy theorists believe they saw a replica of one of Egypt's Great Pyramids on Mars.

Citing the 'near-perfect design and shape', they argued the 'pyramid' is evidence that an ancient civilisation once lived on the red planet.

While the pyramid is believed to be 'car-sized', alien-hunters say it may be just the tip of a much larger structure buried beneath.

YouTube channel, ParanormalCrucible, used video footage taken by Nasa's Curiosity Rover on May 7 to back up its claims.

'None of the Curiosity Rover's subsequent photos taken at 20 to 30 sec intervals in the following few minutes and the subsequent photos hours later, included the object,' wrote UFO site Exopolitics.

'It appears that the Nasa operators of Curiosity deliberately chose not to take another photo or zoom in on the pyramid.

'If they however did so, none of these subsequent photos were released to the general public.'

ParanormalCrucible goes further, claiming the 'near perfect design and shape' means the pyramid is: 'the result of intelligent design and certainly not a trick of light and shadow'.

Commentators on the the channel, however, were not convinced, with some pointing to similar rock formations on Earth caused by wind.

But the story strikes a note with conspiracy theorists who believe that civilisations, including our own, have secretly visited Mars and established colonies there.

In November last year, a woman named 'Jackie' called into American radio station, Coast to Coast AM, with a 'confession' that she had witnessed suited men running on the red planet in 1979.

Jackie said she was working as part of a 'downstairs' team downloading telemetry from a Viking Lander when she saw the humans via live feed.

'I wonder if you could solve a 27-year-old mystery for me,' she asked the presenter. 'That old Viking rover was running around.

'Then I saw two men in space suits - not the bulky suits we normally used, but they looked protective. They came over the horizon walking to the Viking Explorer.'

Nasa did not corroborate the story, but this didn't stop conspiracy theorists from claiming it as evidence for a 'secret space programme.'

According to Jackie, six other Nasa workers saw the two humans walking on the red planet's surface.

Jackie's claim follows a similarly bizarre theory by physicist Dr John Brandenburg who believes an ancient civilisation on Mars was wiped out by a nuclear attack from another alien race.

Dr Brandenburg says ancient Martians known as Cydonians and Utopians were massacred in the attack - and evidence of the genocide can still be seen today.

He claims his theory could explain the Fermi Paradox - namely why, if the universe is abundant with life, we haven't heard anything from anyone else yet.

He warns, though, that we need to be fearful of an attack on our own planet, and should mount a manned mission to Mars to know what we're up against.