Claims that about 100 stray dogs were buried alive in northern China are being investigated, an official said Sunday, the latest apparent case of animal cruelty to shock the nation.

Allegations that a pit pictured online Wednesday containing scores of stray dogs had been filled in by local government officials were made by a charity based in Inner Mongolia.

The Yinchuan Dawn Pets Home group investigated after a woman searching for her pet dog near a garbage dump in Alxa League, near China's border with Mongolia, told them that the animals were trapped on Wednesday.

When the charity visited the site the following day, they found that the pit had been filled in.

A charity volunteer told AFP that another visit was made on Friday, but by then it appeared that the dead dogs had been moved elsewhere, in what the group said was an attempt by local officials responsible for enforcing city laws -- called Chengguan in China -- to hide the grim burial.

"We hired an excavator and found in the place where the dogs were buried six dead dogs which were damaged by an excavator before we got there," the volunteer surnamed Fan told AFP.

"These dogs all had soil in their mouths and noses, which means before we arrived at the scene local Chengguan had already transferred the dogs' bodies to another secret place."

An official from the local Chengguan office denied the allegations and said an investigation had been launched.

"We are investigating if some stray dogs were buried alive," the official told AFP.

"I can ensure you we didn't do this kind of thing, and moreover, we are not in charge of stray dogs."

- Internet outrage -

Pictures of the dogs before the alleged burial were posted by the charity on Sina Weibo -- China's version of Twitter.

The images showed scores of animals in a dusty ditch about six feet (1.8 metres) deep. The original post was followed by subsequent updates detailing the burial claims.

The allegations against the Chengguan -- who have a reputation for brutality in China -- sparked a wave of fury, with some online comments being forwarded tens of thousands of times.

"(We) should put these officials into a pit, no better than a group of beasts," one netizen said in a Weibo post Sunday.

Pet ownership has ballooned across China, with more than 30 million households now keeping a cat or dog, according to research group Euromonitor.

China -- which has no laws against animal cruelty -- has also witnessed an increase in animal rights campaigning in recent years.

In May 2013, dozens of stray cats were slaughtered in a residential district in Beijing, with their fur almost completely plucked out, state news agency Xinhua reported.

Animal rights campaigners in Shanghai highlighted the case of a woman who was alleged to have killed hundreds of cats, the Global Times newspaper reported in 2012.

Official policy in many Chinese cities is that stray dogs are rounded up and found new homes, but activists say they are usually put down or sometimes sold on to restaurants for their meat.