Tens of thousands of protesters in the Macedonian capital Skopje have demanded the resignation of long-serving Prime Minister Nikola Gruevski.
The rally followed the release by the opposition of covert recordings which appear to show ministers plotting vote-rigging and the cover-up of a murder.
Mr Gruevski denies the allegations.
Adding to the political instability, last weekend eight police officers and 14 ethnic Albanian fighters were killed in clashes in the city of Kumanovo.
Crowds gathered outside the prime minister's office in central Skopje. Demonstrators carried both Albanian and Macedonian flags in a show of unity.
Police in riot gear were stationed near the protests.
In 2001, Macedonia came close to the brink of civil war when armed rebels demanded greater rights for the Albanian minority, which makes up about a quarter of Macedonia's 2.1 million population.
The government says the opposition is trying to destabilise the country for its own benefit. It is organising a counter-demonstration for Monday.
At the scene: Guy De Launey, BBC News, Skopje
The front of Macedonia's government headquarters looks fit for an outdoor concert. A stage, big screen and massive sound system are all in place. And so are the people - young and old, ethnic Macedonians and ethnic Albanians - united in their goal.
The head of the main opposition party, Zoran Zaev, says he hopes 100,000 people will attend, but even a tenth of that would send a powerful message, especially as people have been reporting difficulties in travelling from other parts of Macedonia, alleging police interference.
Mr Zaev says the protest will not end until Prime Minister Gruevski resigns. As long as the weather remains warm and dry, waiting should be no great hardship. But despite the resignation of two ministers last week, there is no indication that Macedonia's leader of almost a decade is ready to quit.
Last week two ministers and the head of the intelligence service resigned.
Opposition leaders said intelligence chief Saso Mijalkov and Interior Minister Gordana Jankulovska were behind attempts to control the press, judiciary and electoral officials by tapping their phones.
Opposition leader Zoran Zaev has been releasing a steady stream of recordings since February.
His party accuses the government of wiretapping 20,000 people, including politicians, journalists and religious leaders.
He says that scores of leaked recordings reveal corruption at the highest levels of government, including the mismanagement of funds, dubious criminal prosecutions of opponents and even cover-ups of killings.
He argues that the abuse of power allegations are so serious that the prime minister has to resign and call new elections.
Opposition parties have boycotted parliament since accusing the governing coalition of fraud in the April 2014 election.
But Mr Gruevski, who has won successive elections since 2006, has repeatedly rejected the allegations.
He has accused Mr Zaev of orchestrating a coup at the behest of unnamed foreign spy agencies who, he says, want to overthrow his conservative government.