Opposition supporters have held a rally in Kuala Lumpur to protest against the result of last weekend's Malaysian election, in which the government was re-elected.
The opposition claims the election was fraudulent and says it is considering court action in up to 30 seats.
Prime minister Najib Razak's Barisan Nasional (BN or National Front) coalition won 133 of the 222 parliamentary seats on Sunday.
It was the coalition's worst result in more than half a century. It also failed to regain a two-thirds parliamentary majority that it lost in 2008.
The BBC reports up to 40,000 protesters, many dressed in mourning black, gathered at the demonstration at Kelana Jaya Stadium on Wednesday night to denounce the results. Participants filled the stands and spilled onto the football field.
"This is merely the beginning of the battle between the people and an illegitimate, corrupt and arrogant government," Opposition leader Anwar Ibrahim, 65, told the crowd.
"We will continue this struggle and we will never surrender."
The BN has accused the former deputy prime minister of deliberately choosing a small stadium on the outskirts of the capital as the venue for the rally to ensure it would spill onto the streets.
National Police Chief Ismail Omar told state news agency Bernama on Tuesday the protest was illegal because the organisers did not have a permit.