Riot police have clashed with thousands of protesters in the Macedonian capital Skopje after the main opposition alleged a cover-up over the death of a man in 2011.
The government said 38 police were injured, although many were thought to have suffered from shock.
The crowd gathered outside state buildings calling on Prime Minister Nikola Gruevski's government to resign.
The protest erupted after the opposition revealed leaked recordings.
It was the latest in a series of wire-taps released by Social Democrat leader Zoran Zaev, who has been locked in a power struggle with Mr Gruevski for several months.
Mr Zaev said the audio files showed the prime minister, Interior Minister Gordana Jankulovsa and other leading officials attempting to cover up the death of Martin Neskovski, 22, who was beaten to death by an interior ministry policeman in June 2011.
His death led to weeks of unrest.
The policeman was convicted but the opposition said its wire-taps showed the government had sought to avoid responsibility for the death by blaming him.
Witnesses say the demonstration began peacefully but turned violent late on Tuesday evening.
Nova TV journalist Sashka Cvetkovska said some police had used excessive force on protesters, including women and girls.
"Then some violent groups joined the protesters and it all went wild," she told the BBC.
Police used water cannon and teargas as stones were thrown and containers set alight.
Macedonia's political crisis dates back to last year's elections, when Mr Zaev's centre-left party made allegations of electoral fraud, denounced the government as a dictatorship, and boycotted parliament.
Mr Zaev, who has been charged with espionage, has made allegations that the government has itself been wire-tapping more than 20,000 people, including judges, politicians and journalists.
Mr Gruevski's conservative VMRO-DPMNE has been in power since 2006 and last month the European Union expressed its grave concern at the deteriorating situation in Macedonia, particularly regarding "rule of law, fundamental rights and freedom of media".
The opposition has called for a large anti-government protest on 17 May.