Demonstrators stopped officials from going to work at several key ministries in an attempt to intensify pressure on Prime Minister Yingluck Shinawatra.
The protesters, led by a former opposition MP, want Yingluck to resign to make way for an unelected ‘people's council’ that would oversee reforms to curb the political dominance of her billionaire family.
Their two-month rallies have pushed the government to call snap polls on February 2, but the protesters have rejected the vote in the latest twist of a political crisis that has gripped Thailand since Yingluck's brother Thaksin was ousted in a military coup seven years ago.
Several thousand demonstrators gathered outside the Thai customs department to prevent staff from going to work, according to a few reporters who were present at the scene.
"This is not democracy. It is autocracy, it is a one-man rule," said rally leader Satish Sehgal, railing at former premier Thaksin's alleged stranglehold on the nation's politics.
"There's massive, rampant corruption in this country…nepotism. Our objective is to try and get rid of all this."
Demonstrators also surrounded the ministries of commerce, labour and information and communications technology.
It is a tactic they have deployed several times during the months-long protests, which have so far failed in their goal of forcing Yingluck from office.
Many key junctions remained blocked in the Thai capital with loudspeakers broadcasting bombastic speeches into the city air after protesters launched the shutdown yesterday, causing widespread disruption to Bangkok's central retail and hotel districts.
But the number of demonstrators on the streets appeared to have declined as some returned to work.
The well-organized protest movement has vowed to occupy parts of the city of 12 million people until Yingluck quits, threatening to disrupt the February election which it fears will only return the Shinawatra clan to power.
A hardcore faction of the movement has threatened to besiege the stock exchange and even air traffic control if Yingluck does not step down within days.
Deputy Prime Minister Surapong Tovichakchaikul insisted that the government was still functioning.
He said that the shutdown is expected to last around one week, urging protest leaders to join talks to find a way out of the crisis.