The paper dispensers have reduced waste by 70 percent since they were brought to Temple of Heaven over the weekend, according to the firm behind the device (AFP Photo/WANG Zhao)

A years-long crime spree by Chinese toilet paper thieves may have reached the end of its roll after park officials in southern Beijing installed facial recognition technology to flush out bathroom bandits.

Park managers at the Temple of Heaven, an expanse of imperial landmarks in the capital, spent three years testing ways to foil the toilet looters, including fingerprinting and laser sensors, before they settled on the new technology, which was introduced over the weekend.

Elderly square dancers taking their bathroom breaks on Tuesday were greeted by a robotic voice: "Welcome! Please stand in the recognition zone".

One by one, they obediently positioned themselves on a yellow square marking and watched their faces pop up on a blinking blue screen mounted to the wall. Then the machine dispensed their individual allotment of 60 cm (23 inches) of toilet paper.

If the same individual attempts to collect more bathroom tissue within nine minutes, he or she will be met with a polite rejection: "Please try again later."

Toilet paper crooks have been known to take home entire rolls, smuggling them out in bulging bags that go undetected at the security gates.

The high-tech solution was welcomed by some of the park's regulars.

"It's pretty good, as long as we have enough to use," said Pu Meilang, 68, who takes frequent strolls around Temple of Heaven.

"It thwarts the rule-breakers."

- Desperate measures -

The park has sought to put a stop to toilet paper bandits for years, according to Lei Zhenshan, a marketing manager for Shoulian Zhineng, the Tianjin-based company behind the device.

In 2014, they started experimenting with different ways of tracking toilet paper usage and finally settled on facial recognition -- but not without some internal dispute.

"It seemed a little awkward at first," Lei said, "but we saw that the degree of waste was quite severe, and decided to take this technical approach to correcting people's behaviour."

He said they decided against fingerprinting because people might use all ten of their fingers in turn to maximise rations.

According to Lei, the technology has already reduced waste by 70 percent since it was brought to Temple of Heaven.

The machines, which cost more than 6000 yuan ($869) each, were first introduced in June around the Bird's Nest stadium in the city's Olympic Green.

Though most Temple of Heaven park-goers by the east gate were able to quickly get their bathroom tissues on Tuesday morning, the system was not without small inconveniences.

One woman had a toddler who was too short to reach the camera range.

Another, a 55-year-old who was partaking in a sailor-style group dance, came clad in a full black navy uniform. She had to remove her cap and sunglasses to receive her portion.

Li Zengxiu, 58, came out of her bathroom stall to discover that she would not be granted additional toilet paper to wipe her hands.

But she was happy to make the sacrifice, Li said as she air-dried them instead.

"We're saving paper for the good of the country."

Users on the social network Weibo were more sceptical.

One commenter wrote: "In two days, the facial recognition machine will be taken too."