Officials travelling to Tanzania with Chinese President Xi Jinping went on a buying spree for illegal ivory, an environmental activist group has said.
In a report, the Environmental Investigation Agency cited ivory merchants who said demand from the delegation in 2013 had sent prices soaring.
China denies the allegations, saying it consistently opposes poaching.
Conservationists say demand for ivory is fuelling poaching in Africa.
China is viewed as the biggest market for illegal ivory. The Chinese use ivory in traditional crafts and carvings which are prized as status symbols, correspondents say.
In recent years poaching has increased across sub-Saharan Africa, with criminal gangs slaughtering elephants for ivory.
‘Security checks averted’
The EIA report cited a trader in Tanzania’s main port city, Dar es Salaam, named as Suleiman Mochiwa, who met undercover investigators.
He said that when the Chinese government and business delegation arrived, ivory prices in the local market doubled to $700 (£438) per kilo during the visit.
“The [delegation]… used the opportunity to procure such a large amount of ivory that local prices increased,” the report says.
Investigators alleged that the Chinese buyers could take advantage of a lack of security checks for those in the country on a diplomatic visit.
“The two traders claimed that a fortnight before the state visit, Chinese buyers began purchasing thousands of kilos of ivory, later sent to China in diplomatic bags on the presidential plane,” the report added.
“When your president [Xi Jinping] was here… many kilos go out… many kilos. Half of his plane go with that,” one of the traders told the EIA investigators.
The trip was Xi Jinping’s first foreign tour as head of state.
Traders told the group that similar ivory sales took place on an earlier trip by China’s former President Hu Jintao.
“The report is groundless, and we express our strong dissatisfaction,” Chinese foreign ministry spokesperson Hong Lei is quoted as saying by the Associated Press news agency.
The director of China’s endangered species import and export management office also dismissed the claims: “Allegations without evidence are not believable,” Mr Meng Xianlin said.
The ivory trade was banned in 1989 by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (Cites). Both China and Tanzania are signatories.
China does have about 150 legal, government-licensed ivory shops, which sell ivory collected prior to this. They are the only places allowed to sell ivory to individual buyers.
Earlier this year China for the first time destroyed a large quantity of confiscated ivory, in a public event described by conservation groups as a landmark move.
Just over six tonnes of carvings, ornaments and tusks amassed over the years were fed into crushing machines.
Nevertheless officials warn that demand for ivory across Asia has led to thousands of elephants being killed in Africa.