A retired Kiwi engineer has been arrested over an alleged hoard of dozens of illegal weapons and explosives that he began collecting after his wife died.

New Zealander Gareth Alan Davies, 63, was detained in a house in the Kathu district of holiday island Phuket in Thailand on November 7 after an arrest warrant was issued against him by the provincial court.

Police claimed they found seven rifles - including an AK and M16 - 19 handguns, 11 grenades and a stash of ammunition in the property.

He was remanded in custody at the Kathu Police Station for charges of illegal possession of firearms.

Police Lieutenant General Surapong Thanomjit, commander-in-chief of the Region 8 Police, said: 'Thank you to the residents who provided information that led to this investigation.

'It has been discovered that the firearms were traded online.

'The arrested person is an engineer who is knowledgeable about mechanical matters and can make certain devices from the components of firearms, including non-licensed firearms.

'He claimed to be collecting bombs, but his collection is prohibited by the law.

The officer said that Gareth had bought items online and modified many of them.

He added: 'This residence is not the only source of modification and production of the firearms for this house. A forensic unit must accompany investigators for a thorough examination.'

Police said the ex-pat has been living legally in Thailand for 23 years. He was married to a Thai woman, Pannee Chanbamrong, for two decades until she died in 2017.

Gareth had been living an unassuming life in the Southeast Asian country and his criminal records also turned up clean as he had never been on any blacklist or watchlist.

He formerly worked lawfully as an engineer on drilling barges in the sea in southern Thailand until he retired at age 55.

His is staying legally in Thailand on a retirement visa until November 2023.