Thai customs have confiscated 21 rhino horns with an estimated value of nearly $US5 million ($6.6 million) in the biggest such seizure in Thailand for years, officials said on Tuesday.

Thailand has become a major transit point for the trade in endangered species to other Asian countries.

Thai customs officers with almost $6.6 million of seized rhino horns at the customs office in the Suvarnabhumi airport, Bangkok. Credit:AP

The seizure of the nearly 50 kilograms of rhino horn came days after 300 kilograms of elephant ivory was impounded and a month after the discovery of almost three tonnes of pangolin scales destined for Laos.

"It's the biggest confiscation of rhino horns in five to 10 years," said Somkiat Soontornpitakkool, director of Thailand's Wild Fauna and Flora Protection division.