A French couple could face up to six years in jail after they were caught with 40kg of sand from a beach in Sardinia in their car.

The pair said they were taking it back as a souvenir and did not realise it was a crime.

It was taken from the beach of Chia in the island's south and put into plastic bottles.

The bottles were found by police in the boot of their vehicle when they were getting on the ferry back to France.

Italian news agency Ansa said they face a theft charge, with the aggravating circumstance of having stolen an asset destined for public utility.

On 1 August 2017, taking sand from Sardinia became punishable.

Authorities got tougher with tourists, issuing fines of up to €3,000, after receiving years of complaints from islanders about sand being taken.

A Facebook page called "Sardinia robbed and plundered" was set up by locals there in 2015 to share accounts of sand being stolen, two years before the new law came into force.

The social media platform was used over the years to press local politicians to act on what they described as an environmental emergency.

The group, with more than 30,000 followers, still actively post examples of souvenir sand being taken and said Sunday that the current policy is not working enough to prevent it happening.