Six tonnes of illegal ivory were seized en route to Hong Kong between 2000 and 2013, while three tonnes being trafficked out of the city illegally were intercepted, a green group has found.
The findings of wildlife trade watchdog Traffic come as the Agriculture, Fisheries and Conservation Department prepares to incinerate the first batch of its 30-tonne ivory stockpile today.
"It means the ivory at one point was either sitting in a container in Hong Kong from somewhere else or sourced from a market in Hong Kong," said Dr Yannick Kuehl, Traffic's regional director for east and south Asia.
Traffic came up with its findings after scrutinising trade statistics from the Elephant Trade Information System, a global database the watchdog runs for the Convention on International Trade in Endangered Species.
A spokeswoman for the Customs and Excise Department said it had been taking stringent action on the illegal trade and had played an active role in international efforts to stop ivory smuggling.
About eight tonnes of ivory were seized last year, up from 5.5 tonnes the year before, according to the department. In July, more than 1,000 tusks weighing nearly 2.2 tonnes and worth HK$17.5 million were found in a shipping container.
Traffic and WWF-Hong Kong highlighted the findings on the eve of the burning as more proof that the city is still one of the world's biggest transit hubs and markets for contraband ivory.
Hong Kong customs seized 33 tonnes of illegal ivory from 2000 to 2013. Three of its biggest hauls were made last year.
WWF programme development officer Cheryl Lo said the figures put the city fifth in the world in terms of quantity of ivory seized since the global trade in ivory was banned in 1989. It placed behind mainland China, Tanzania, Kenya and Namibia.
"Geography certainly plays a role given that the mainland is the world's biggest consumer in the world for ivory and about half of [all] illegal ivory heads to there and the rest to Thailand or other parts of east Asia," Lo said.
She welcomed the move to destroy the stockpile but called for tighter monitoring and control over the legality of ivory sold on the local market and audits of any stock to be destroyed to ensure transparency.
Kuehl said law-enforcement techniques needed to include forensic examinations of seizures, profiling of criminal activity and targeting of cargo from high-risk countries.
The stash of seized ivory in Hong Kong is understood to be the world's largest to be destroyed. Its destruction will take two years, as no more than three tonnes can be burned at one time. Ouf of the stash, 1.6 tonnes will be kept by the department for education or scientific purposes. About 6.5 tonnes was destroyed last year as the government tried out disposal methods.