A huge haul of illegal ivory in China has revealed the vast scale of the trade and flaws in the country's system of legal ivory sales, a wildlife monitoring group said.

A court heard that authorities seized a total of 7.7 tonnes of ivory on a series of occasions in 2011, reports said last week, and three people were jailed for terms ranging from seven to 15 years in connection with the case.

The seizure represented the ivory of more than 800 elephants, wildlife monitoring group Traffic said in a statement.

China has a legal market in ivory, which is supplied from a stockpile of 62 tonnes of ivory bought with international approval in 2008. But critics have accused the legal trade of masking a much larger illegal market.

One of the convicts managed several legal ivory shops, showing a systematic attempt to "launder illegal ivory into the legal marketplace on a grand scale", Traffic said.

"The magnitude of these seizures is a shocking blow to the integrity of China's legal ivory trade system," the release quoted Traffic spokesman Tom Milliken as saying.

The group added that the Chinese report brought the total estimated weight of ivory seized in 2011 to a "staggering" 46.5 tonnes, making it the worst year for ivory smuggling on record.

"2011 was already the worst year for the volume of ivory seized since records were first compiled in 1989, but this new information puts the annual total into the astronomic zone," Milliken said.

Conservation group WWF estimates that around 25,000 elephants were hunted for ivory in 2011, and predicts an even higher toll for 2012. There could be as few as 470,000 left, it says.

Experts say that most illegal ivory is taken to China, with some estimating the country accounts for as much as 70 percent of global demand.

But conservation groups have also praised China for making high-profile arrests of major ivory smugglers.

"Authorities in China are to be congratulated for this breakthrough," Traffic said in the statement Friday, "but must endeavour to follow up on every possible lead to ensure this ivory supply line between Africa to China is well and truly severed."