Thai police say a key suspect in the Bangkok shrine bombing has confessed to giving a bag containing a device to the man who carried out the attack.

National police spokesman Prawut Thavornsiri's announcement came as the suspect, Yusufu Mieraili, was taken to a train station in Bangkok to re-enact the alleged handover.

The 17 August blast at the Erawan Shrine killed 20 people.

Two foreign men are in custody, but the bomber himself has not been found.

The man, wearing a yellow T-shirt, was seen placing a backpack at the popular shrine and leaving, shortly before the explosion.

'It was a bomb'

Prawut told reporters at the Hua Lamphong station in Bangkok: "This is the area where he met the man in a yellow shirt to exchange the backpack."

"Yusufu said the backpack that he carried was heavy and it was a bomb," he said.

Mieraili, who has not been charged, was intercepted earlier this month as he attempted to cross the border into Cambodia.

Police have not confirmed his nationality but say he was carrying a Chinese passport.

On Tuesday, he was taken to visit two apartments in other parts of Bangkok where police said they found bomb-making materials as well as passports.

The other man in custody has been named by local media as Adem Karadag.

Local media have quoted police sources as saying that they are hunting for the alleged mastermind of the attack, who is thought to have left Thailand a day before the attack.

Police also released a photo of the man, who was named as 27-year-old Abudureheman Abudusataer, also known as "Izan" or "Ishan".