Supporters linked to the red-shirt movement began gathering outside Klong Prem Central Prison on Sunday, setting up camp along Ngam Wong Wan Road as they await the scheduled parole of former prime minister Thaksin Shinawatra on Monday.
Groups from several provinces arrived on Sunday, some pitching tents and laying down mats to stay overnight, while others set up stalls selling food, drinks, clothing and souvenirs.
Security was tightened around the prison, with the Metropolitan Police Bureau deploying more than 50 crowd control officers to maintain order from Sunday through to noon on Monday. They were working in rotating shifts, according to Thai PBS.
The Corrections Department also assigned more than 50 officials to the area and was coordinating with supporters to keep them away from the prison perimeter, to ensure their safety.
Inside the prison compound, metal barricades have been installed near the flagpole circle at the entrance, organising space for news reporters and members of the public expected to follow developments on Monday.
Thaksin, 76, is due to be freed on parole on May 11 after being granted early release under general parole criteria. He was returned to prison late last year after the Supreme Court ruled his lengthy stay at the Police Hospital could not be counted towards his sentence.