Police are investigating after three Chinese tourists were filmed destroying an ancient stalactite formation in north China.

Surveillance footage of the incident at the Yishui Underground Gallery in Shandong province shows the unruly visitors smashing the million-year-old limestone formation with a large rock before breaking a piece off each.

The three men, all in their 50s, walked away with the broken pieces of rare dripstones as souvenirs, according to Chinese reports.

Surveillance footage of the incident at the Yishui Underground Gallery in Shandong province on April 21 shows the unruly visitors smashing the million-year-old limestone formation with a large rock before breaking a piece off each

The footage shows one of the men was walking along the cave's main path before spotting the dripstone at about 2:10pm. He then picked up a large rock and started smashing the limestone

The damaged section of the stalactite in the cave attraction. The destroyed section took nature about one million years to form, according to Yang Feng, the manager of the site

Staff members of the cave attraction called police on April 21 and the men are yet to be found, according to China Youth Daily.

'The three men thought the dripstones were very beautiful and damaged them. The destroyed piece was about 10cm wide and 20cm long,' Yang Feng, the manager of the Yishui Underground Gallery told video news site Pear.

The entire piece of stalactite exhibit, titled 'A Pair of Lovebirds', took nature about four million years to form, Yang said.

The part that was snapped off alone took about one million years to form, he added.

'The three men thought the dripstones were very beautiful and damaged them. The destroyed piece was about 10cm wide and 20cm long,' said Yang

As the three walked further along the attraction, they damaged another section of the cave

Staff members of the cave attraction called police on April 21 and the men are yet to be found

The footage shows one of the men was walking along the cave's main path before spotting the dripstone at about 2:10pm.

He then picked up a large rock and started smashing the limestone. When he wasn't able to break it off, he turned to hit a different section, which broke off after one strike.

He then showed it to his friends, who hurried and copied his act of vandalism. They ended up breaking off two pieces of the formation each.

Yang said as the three walked further along the attraction, they damaged another crystallised section of the cave.

Yang says it takes a painstakingly long period of time for the stalactite to be formed, produced by the the precipitation of minerals from water dripping through the cave ceiling

Social media users were quick to condemn the men with one comment suggesting tourists should be banned for the bad behaviour. Above, police investigating the damaged section

He said it takes a painstakingly long period of time for the stalactite to be formed, produced by the the precipitation of minerals from water dripping through the cave ceiling and restoration is not an option.

Chinese social media users were quick to condemn the men with one comment suggesting tourists should be banned for the bad behaviour.

'Tourists spots should hang up their pictures at the entrance!' one user said.

'They should be thrown in jail to let everyone know the consequences of such uncivilised behaviour!'

The picturesque Yishui Underground Gallery, with a total length of 6.6 kilometres (4.2 miles), was discovered by villagers in 1999, according to reports

Each formation has been given monikers according to animals they are said to resemble, such as 'dragon flying in the sky', turtle scouting the sea', and eagle over the mountains'

Yishui is home to hundreds of natural karst caves and is known as the largest karst cave cluster in terms of scale in north China

The picturesque Yishui Underground Gallery, with a total length of 6.6 kilometres (4.2 miles), was discovered by villagers in 1999, according to reports.

Each formation has been given monikers according to animals they are said to resemble, such as 'dragon flying in the sky', turtle scouting the sea', and eagle over the mountains'.

Yishui is home to hundreds of natural karst caves and is known as the largest karst cave cluster in terms of scale in north China. The caves range in length from several hundred meters to nearly 10 kilometers (6.2 miles), according to China Daily.