Two African leaders torched five tonnes of seized ivory on Wednesday as an international conference on tackling illegal exploitation of wildlife opened in the Republic of Congo.

Congo's President Denis Sassou Nguesso and his Chadian counterpart Idriss Deby set the stock of elephant tusks on fire in the capital Brazzaville.

"We are drawing a line and this is a break with a sad past. From now on, we will be harder(on poachers)," said Congo's Forest Industry and Sustainable Development Minister Henri Djombo.

Authorities in Congo have in the past claimed that poaching is still a "minor phenomenon" because the elephant population has increased from 10,000 in the 1980s to over 40,000 today.

In Africa as a whole however, the elephant population is under threat -- there are 450,000 left today compared to 1.2 million in the 1980s.

"Burning five tonnes of ivory is relatively large, but it is a small amount when you consider the amount that is trafficked globally," Stephanie Vergniault, president of SOS Elephants, told AFP.

"This destruction is a message to consumers and ivory traffickers."

Kenya in March burned 15 tonnes of elephant ivory -- worth about $30 million (27 million euros) on the black market -- and vowed to destroy its entire stockpile of illegal tusks by the end of the year.

Ministers from Africa and global experts are meeting in Brazzaville to discuss strategies to stem unregulated logging, poaching and smuggling of animals.

Elephant hunting is often organised by international criminal networks to supply the illegal ivory market, mainly in Asia, with some profits thought to fund regional conflicts and militants.

The value of illegal activities ranges from anywhere between $70 billion to $213 billion annually, according to a 2014 joint UN and Interpol report.

"Global environmental crime... is helping finance criminal, militia and terrorist groups and threatening the security and sustainable development of many nations," the report said.

Last month, conservation experts met in Botswana, issuing dire warnings over the booming illegal wildlife trade that threatens the survival of not just elephants, but rhinos, tigers and other endangered species.