Tunisia's president sacked the prime minister on Sunday and froze parliament, in a move critics have called a coup.
President Kais Saied joined tens of thousands of his supporters that thronged the streets of the capital Tunis in the evening.
Fireworks were set off while the crowds cheered in scenes recalling the Arab Spring protests a decade ago, which introduced a democratic system to the country.
Saied on Sunday laid out a number of other decisions, in addition to dismissing the government.
"The first decision is to freeze all the powers parliament."
"The second decision is to lift the immunity of all members of parliament."
"The third decision is that the president assumes the executive authority with the help of a prime minister appointed by the president of the republic."
In the early hours of Monday, the military barred Parliament speaker Rached Ghannouchi from entering the parliament building.
In a phone call to Reuters, he called the president's decisions 'a coup against the revolution and constitution'.
He rallied his supporters to take to the streets, though President Saied warned against any violent response.
Protests that erupted along with Sunday's celebrations were directed at the moderate Islamist Ennahda Party, the biggest in parliament.
Once banned before the 2011 revolution, that party had been the most consistently successful since then, and a member of successive coalition governments.
But anger against the government has been simmering in Tunisia for years, brought on by corruption, declining state services, and growing unemployment.
It was not immediately clear however how much backing the president's decisions have.