At the city hall, in Muang district, the doors of all offices have been chained and locked up by protesters with the People's Democratic Reform Committee (PDRC). The closure will continue until tomorrow.
All hospitals and police stations have been allowed to remain open to provide medical services and maintain law and order.
Government offices in Hat Yai, the commercial centre of the province, and Sadao districts have also been closed.
Pongsapak Wuthipunya, a PDRC core member in Songkhla, said the protesters would continue with their campaign for reforms before an election, particularly on advance voting day, this Sunday, and election day, Feb 2.