Poachers have killed a record 405 rhinoceros in South Africa since the start of the year, the national park board said on Tuesday.

"The number of rhinos poached is up by approximately 21.6 percent from the 333 of the previous year," said South African National Parks (Sanparks) in a statement posted on its website.

Rhino killings have spiked from 13 in 2007 as poachers hunt for rhino horn, made of the same substance as human fingernails.

It is popular for use in Asian medicinal treatments -- especially in China and Vietnam, where it is believed to cure cancer despite scientific evidence to the contrary.

Authorities arrested 210 people for poaching in 2011, compared to 165 in 2010, according to Sanparks.

Booming demand has driven the price up to record levels of half a million dollars for the largest horns, according to the Convention on International Trade in Endangered Species.

South Africa has responded to the surge by dispatching army troops to fight poachers and stepping up arrests.

But it has struggled to stop poaching syndicates that use helicopters, night vision equipment and high-powered rifles to hunt their prey.