Image copyrightAFP/GettyImage caption The haul accounts for 20% of Hong Kong's rhino horn seizures in five years Airport authorities in Hong Kong have arrested two men smuggling a record number of suspected rhino horns worth $1m (780,000) on Thursday.Some 24 severed rhino horns weighing 40kg (88lb) were found in the bust - Hong Kong's largest ever seizure.The alleged smugglers were in transit to Ho Chi Minh City in Vietnam from Johannesburg in South Africa.Customs officials said the illegal haul was brazenly transported through the terminal in two cardboard boxes.The airport incident comes just two weeks after Hong Kong seized a record eight tonnes of pangolin scales and more than 1,000 elephant tusks.A local environmental group said Thursday's rhino horns accounted for 20% of the total amount of Hong Kong's rhino horn seizures since 2013.Hong Kong is a known transit point for the illegal wildlife trade, and conservation groups have urged the authorities to crack down on smuggling.Rhino horn is used in China and Vietnam in some traditional medicine, despite containing little more than keratin, the same protein that makes human hair and fingernails.The demand for rhino horn has fuelled wildlife poaching, particularly in South Africa, which is home to about 80% of the world rhino population.Conservation groups say the number of rhinos killed has been gradually decreasing since 2014, but more than 1,000 rhinos continue to be killed in South Africa every year.