Hong Kong customs officers seized almost four tonnes of ivory worth about $3.4 million, hidden in shipments from Kenya and Tanzania, officials said Saturday.

The 1,209 pieces of raw ivory tusk and a small number of ivory ornaments were discovered in two containers marked "plastic scrap" and "roscoco beans", shipped to Hong Kong earlier this week, a customs official said.

The smuggled ivory, weighing 3.81 tonnes (8,400 pounds) -- Hong Kong's largest ever seizure -- was found hidden among bags of plastic scraps and beans by customs officers acting on a tip-off from counterparts in mainland China.

"The total seizure is worth about HK$26.7 million ($3.4 million)," the Hong Kong customs department said, adding that it will step up efforts with mainland Chinese authorities to combat transnational smuggling activities.

Mainland Chinese authorities arrested seven individuals, including a Hong Kong resident, in relation to the seizure, public broadcaster RTHK said.

Under Hong Kong law, anyone found guilty of importing unmanifested cargo into the southern Chinese city -- a major shipping hub -- faces imprisonment of up to seven years and a maximum fine of HK$2 million.

In addition, those guilty of importing, exporting or possessing an endangered species for commercial purposes face up to two years in jail and a maximum HK$5 million fine, customs officials said.

The international trade in elephant ivory, with rare exceptions, has been outlawed since 1989 after elephant populations in Africa dropped from millions in the mid-20th century to some 600,000 by the end of the 1980s.

However, a rise in the illegal trade in ivory has been fuelled by demand in Asia and the Middle East, where elephant tusks are used in traditional medicines and to make ornaments.

Africa is home to an estimated 472,000 elephants whose survival is threatened by poaching, illegal game hunting and habitat loss.