A German tourist has been arrested for stealing a pair of designer sunglasses from a Russian woman at an immigration office in Thailand.

Marcel Albert Mohr, 31, was seen on CCTV walking into the building shortly after Viktoriia Duka, 37, left with her passport stamps on the island of Koh Pha Ngan on February 9.

After being handed her documents, she and her companion stood up to leave, but forgot the expensive McQ brand sunglasses worth 24,000 THB (around 710 USD) on her seat.

Russian national Viktoriia Duka, 37, was at the Immigration Bureau at Koh Pha Ngan in Surat Thani province to have her visa extended on February 9.

Minutes later, Marcel appeared wearing a black and white checkered shirt and, seeing the forgotten accessory lying unattended, swiftly pocketed it before exiting the scene.

A frantic Viktoriia later returned to the office, but could not find the missing eyewear. She reported its disappearance to the police.

Upon checking the CCTV footage, they were able to identify the suspect as Marcel Albert Mohr, 31, who was staying at a resort on the island.

The following day, officers arrived at the German's lodging and searched his room. He was wearing the same shirt and police found Viktoriia's black sunglasses stashed in his bag, prompting him to admit to the theft.

He told cops he did not know whom the shades belonged to, so he took it for himself.

Marcel said: 'I just thought that someone had left them and forgotten about them. I didn't think there would be any problems. I didn't know they were valuable or I was breaking the law.'

Marcel was detained by police and fined for theft before being released.