SURAT THANI: A local fisherman has asked authorities to help verify whether a large lump of material he found on an island beach is indeed ambergris and worth about 10 million baht.

Koh Phaluay resident Jamras Thiachote, 55, showed the six-kilogramme lump to Surat Thani governor Wichawut Jinto, who visited the island in Koh Samui district yesterday.

Brown and gold in colour, the object looks like a rock but floated when it was placed in a bucket of water.

Mr Jamras said he came across the lump on a beach on Jan 3 after Storm Pabuk passed over the island. He had no idea what it was and so left it there. A young relative then searched the internet and announced it was ambergris, prompting Mr Jamras to return and retrieve the object.

"When I cut it with a knife, it gave off a fishy smell for a moment," the fisherman said.

Learning of his discovery, three people in the village asked for a 500-gramme slice, claiming they would verify whether it was ambergris. "I have not heard anything from them since," Mr Jamras said.

A park ranger on Koh Phaluay told him his find was likely to be ambergris, while locals speculated that a lump that size was worth about 10 million baht.

Ambergris is a highly valued waxy substance produced by sperm whales. It is prized as a perfume ingredient.