Thousands of Thai demonstrators gathered outside four ministries in an effort to cripple the administration and oust prime minister Yingluck Shinawatra.
Protesters also gathered at a major government office complex and 19 provincial halls.
The Department of Special Investigation was evacuated as about 2,000 protesters rallying against Ms Yingluck and her influential brother, former prime minister Thaksin Shinawatra, surrounded the crime agency in a Bangkok suburb.
The demonstrations have been going on for weeks but are expanding and gaining momentum.
Five ministries in the capital were evacuated in the past two days and protesters are occupying the finance ministry.
Groups of demonstrators gathered in front of the ministries of labour, energy, health and commerce in Bangkok, as well as local government offices in 19 provinces.
The anti-government protesters, led by Suthep Thaugsuban, a deputy prime minister in the previous government, chanted abuse at the DSI.
Dozens of riot police scrambled to put on helmets and hold up shields as crowds pushed against a low fence.
The DSI shares the compound with important government agencies, including tax, revenue, immigration and land departments.
Some employees were seen leaving their offices and joining the demonstrations.