A 20m-long (65ft) underground escape tunnel has been discovered at an immigration detention centre in Australia, refugee campaigners say.

The tunnel, at the Yongah Hill detention centre near Perth, was reportedly within five metres of the site's perimeter when it was found.

More than 300 people, including asylum seekers and criminals facing deportation, are living at the site.

Immigration officials have not yet commented on the reports.

The tunnel, said to be three metres deep, led from a room in one of the accommodation blocks and went past two inner fences, towards the outer fence, said the campaign group Refugee Action Coalition.

According to ABC News, a number of detainees were moved to another part of the facility after the discovery.

Chris Antonio, the Shire of Northam president, told ABC the tunnel was only 2.4m long. "As far as we're aware, the situation is contained and we're also aware that there weren't any escapees, it was just an attempt," he said.

It was unclear how many people were behind the construction of the tunnel and Australian border force is yet to comment on the incident.

According to Border Force statistics, there are currently 320 men detained at Yongah Hill. Refugee Action Coalition says 140 of them are asylum seekers.

The campaign group said that the average time spent in detention is now over 600 days, though many of the asylum seekers are long-term detainees who have been held for over five years.

In 2013, five Vietnamese men are thought to have escaped from Yongah Hill by scaling the centre's fence.