Up to 6.5 tonnes of seized ivory has already been destroyed as the government tests out the most efficient way to dispose of the city's enormous stockpile.
The amount destroyed was about 17 per cent of the 37.8 tonnes of ivory confiscated from 1976 to last year.
Most of it was burned in incineration trials last year at the Tsing Yi chemical waste treatment plant, but a small amount was crushed to see if it could be used in cement.
The information, released by the Agriculture, Fisheries and Conservation Department on Wednesday, explains the shortfall in figures when the government announced last month that it would be burning 28 tonnes of stockpiled ivory but withholding 1.6 tonnes of tusks for science and educational purposes.
The department said that it had also donated 1.7 tonnes of ivory for purposes allowed under the internationally agreed Convention on the International Trade in Endangered Species of Wild Fauna and Flora.
A spokeswoman did not explain why 6.5 tonnes of ivory was necessary to conduct the trials. "The figure covers trials of various methods of destruction including incineration, stabilisation [of cement] and crushing by mechanical means," she said.
Richard Thomas, a spokesman for wildlife trade monitoring network Traffic, said the amount used seemed huge but he also noted the complexity of the process. He said tests in America found only the surface of the tusks charred when burned for 30 minutes at 1,000 degrees.
Dr Paul Shin Kam-shing, chairman of the Endangered Species Advisory Committee that made the decision to destroy the ivory, said it was hard to judge if 6.5 tonnes was an excessive amount. He said: "Officials have never told us how much they incinerated in the trials." Shin also disagreed with suggestions that the department's handling of the ivory should arouse suspicion.