Jakarta (AFP) - Hundreds of slow lorises have been seized on Indonesia's Java island as animal smugglers were about to send the protected primates to markets to be sold as pets, officials said on Friday.

Government officials last week discovered 238 of the nocturnal animals, one of the few mammals that has a toxic bite, packed into small plastic crates at the port of Merak in the north-west of Java.

They had been smuggled from Sumatra, a vast, jungle-covered, biodiverse island that is home to many rare animals, said protection group the International Animal Rescue Foundation Indonesia.

The group took them to their rescue centre but on the way "six of them died... because they were squeezed tight in the crates and lacked food and water," the foundation's Aris Hidayat told AFP.

The animals were about to be sent to markets in the capital Jakarta and surrounding cities when they were rescued, Hidayat said.

Vets at the rescue centre believe the animals had only been captured recently and said hopefully they could be released back into the wild soon, he said.

The Natural Resources Conservation Agency, the government body that discovered the lorises, said a man had been named a suspect in the case and would face trial soon.

Under Indonesian law, someone caught selling protected animals faces a maximum of five years in jail and a 100 million rupiah ($8,700) fine.

The slow loris, which has big eyes, grey fur and is closely related to the lemur, is found across Southeast Asia.

The International Union for Conservation of Nature categorises the lorises on Sumatra as vulnerable.