Led by Suthep Thaugsuban, secretary-general of the People’s Democratic Reform Committee, protestors started around 10 a.m. a march of about eight km in downtown Bangkok, Xinhua reported.
Similar warm-up rallies will take place Tuesday and Thursday.
The operation to shut down Bangkok may last from five to 20 days to pressure caretaker Prime Minister Yingluck Shinawatra to step down, Suthep said.
In the meantime, pro-government Red Shirts are also planning to gather Jan 13 to counter the Bangkok shutdown, but they will avoid the capital and the neighbouring and southern provinces so as not to conflict with protesters, according to Red Shirt leader Natthawut Saikua.
The ruling Pheu Thai Party has already started its campaign in five provinces for the Feb 2 general election, which the Election Commission (EC) said earlier would proceed as scheduled.
Constituency-based candidate registration for the election, which concluded last week, was blocked in 28 constituencies in eight southern provinces, but the EC said it was not empowered to extend the registration period or postpone the election.