This is the tunnel unearthed at a high-security jail in Argentina built in a secret plot to spring a notorious drugs catel boss serving a 33-year sentence.

The tunnel stretching 300 metres was discovered by guards who found its exit in a ramshackle hut outside the walls of the General Roco prison in Rio Negro on April 6.

Video footage and photos show its walls were shored up with scrap wood from crates, packing cases and pallets.

A makeshift ladder led up to the hut and a collection of shovels, picks, buckets and flares can be seen lined up on the tunnel floor.

One suspect, who has not been named, was arrested when he was found inside the hut and has reportedly been charged with aiding and abetting criminals to escape.

Local media reported that the tunnel's mastermind was Ramon Forno, the brother of a gang leader who was serving 33 years behind bars.

It is unclear whether Forno was the suspect arrested at the hut and there were no details about whether any prisoners escaped before the tunnel at Prison No. 2 was found earlier this month.

The governor of Rio Negro, Alberto Weretilneck, said: 'I want to recognise the bravery and professionalism of our Rio Negro Police personnel who this afternoon prevented the possible escape of inmates from the General Roca Prison.

'Thanks to all the personnel of the force who give their best every day to take care of the people of Rio Negro.'

Officers said that the investigation is ongoing.