Major intersections in the capital Bangkok were blocked for a second day, and a hardline faction of the agitators threatened to storm the stock exchange.
Protest leaders say demonstrators will occupy the city's main arteries until an unelected "people's council" replaces Prime Minister Yingluck Shinawatra's administration, which they accuse of corruption and nepotism.
Analysts said the scope for a peaceful resolution of the crisis ahead of elections next month was narrowing.
The International Crisis Group (ICG) think-tank said in a report "There is no clear way out."
Ministries and the central bank have been forced to operate from back-up offices after protesters led by Suthep Thaugsuban stopped civil servants getting to work.
He said: "In the next two or three days we must close every government office. If we cannot, we will restrict the movements of the prime minister and other ministers. We will start by cutting water and electricity to their homes. I suggest they evacuate their children."
A student group allied to Mr Suthep's People's Democratic Reform Committee (PDRC) also threatened to attack the stock exchange.