Hundreds of thousands of protesters have taken to the streets of Prague demanding that PM Andrej Babis resign.
Mr Babis is facing a criminal investigation over alleged fraud, and is also the subject of an EU conflict-of-interest investigation. He denies the allegations.
Organisers say about 250,000 people attended the rally. The figure could not be verified.
It is said to be the largest protest since the fall of communism in 1989.
The protest was organised by the Million Moments for Democracy group. The movement has grown from a small student initiative into a mass movement.
It has organised a number of protests this year. The last major rally was on 5 June when 120,000 people marched in the capital.
At the rally, Mikulas Minar, the head of the protest group, told AFP news agency: "Judging from the aerial photos, it looks like we're about 250,000. We'll see how many more will arrive."
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