Hong Kong on Thursday began destroying nearly 30 tonnes of ivory seized from smugglers in the world's largest such operation, a major step in the fight against the illegal trade in elephant tusks.

The move to incinerate a stockpile seized since 2003 comes after intense pressure from conservation groups.

"Today's ceremony sends a loud and clear message to both the local and the international community that the Hong Kong government is determined to curb illegal trade in elephant ivory," the city's environment secretary Wong Kam-sing told reporters.

"We hope curbing illegal trade in ivory will help stop illegal poaching of elephants," Wong said at a treatment plant in the city's Tsing Yi district, where the first tonne of elephant tusks were destroyed on Thursday.

The tusks were broken down into smaller pieces before being burned in an incinerator. The charred remains will be sent to landfill.

The global ivory trade has been banned under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) since 1989.

But millions of dollars worth of tusks are smuggled out of Africa each year, fuelled by demand in China and other Asian countries where statues, trinkets and other items made from ivory are seen as status symbols.

Ivory tusks and products such as sculptures and chopsticks were displayed at the Hong Kong ceremony where officials wearing turquoise overalls, face masks and helmets carried containers filled with tusks to the incinerator.

Authorities plan to destroy 28 tonnes of ivory over the course of a year.

Hong Kong has traditionally been a major hub for the illegal ivory trade, with tusk seizures rising steadily since 2009, reaching a record of 8,041 kilograms in 2013.

"Hong Kong holds one of the largest stockpiles of seized ivory in the world," CITES secretary general John Scanlon told reporters.

The destruction "sends a powerful message that Hong Kong does not accept, and will not tolerate this illegal trade", Scanlon said.

- 'A moral and necessary step' -

City authorities have seized a total of 33.37 tonnes of ivory since 2003, most of which had been smuggled from Africa by sea.

Some 400 kilograms of the stockpile has been donated to schools for educational purposes, and some has already been incinerated in test runs.

Hong Kong ranks fifth in the world in terms of the quantity of ivory seized from 2000 to 2013, according to the Elephant Trade Information System database.

Environmental groups welcomed the destruction of the Hong Kong haul as a major step in the battle against poaching.

"Hong Kong's leadership could save Africa's elephants," said Iain Douglas-Hamilton, founder of the conservation group Save the Elephants.

The African Wildlife Foundation said the Hong Kong operation was "a moral, and necessary, step in halting the ongoing slaughter of Africa's elephants".

Hong Kong's move follows similar ivory destruction operations by other governments, including in China and France.

Experts believe that China accounts for as much as 70 percent of global demand, with a growing middle class coveting status symbols made from ivory.

Some 22,000 African elephants were killed illegally in 2012, according to a report last year by the International Union for Conservation of Nature, which warned of "local extinctions if the present killing rates continue".