Hong Kong's leader has vowed to punish protesters who attacked policemen outside world trade talks on Saturday.
Protesters chanted 'Down with WTO'
Donald Tsang was speaking after meeting police officers in Wan Chai district hours before demonstrators gathered for another - largely peaceful - protest.
About 900 people, many South Korean farmers, were arrested after Saturday's clashes that injured more than 70.
South Korea's foreign ministry is to "make its best diplomatic effort" to release them, AFP news agency reports.
It quoted a statement by Prime Minister Lee Hae-chan expressing concern over the arrests - adding that Deputy Foreign Minister Lee Kyu-Hyung was to fly to Hong Kong on Monday to deal with the issue.
In the latest demonstrations, activists gathered in an area near the talks venue the police had sealed off ready for protests.
The defences there have been reinforced with heavy stone blocks piled up on both sides of the road to the conference centre. Between them sit armoured vehicles equipped to fire teargas grenades.
The march was led by local activists followed by a small group of Korean farmers.
The protesters lit a small fire in front of the police lines as darkness fell.
Chanting "Down, down WTO", they listened to speeches in the presence of reinforced police, who say they are taking no chances.
Most of those held after Saturday's clashes - the worst violence in Hong Kong since 1989 - are South Korean farmers.
"All the people we have apprehended, we have apprehended according to the law of Hong Kong. They will be dealt with according to the law of Hong Kong," said Donald Tsang.
"Against [those] whom we have evidence that they have caused violence and attacked policemen and law enforcement agencies we will take them before the court. Those [for whom] we have no sufficient evidence we will release them.
"I think we have done and demonstrated to the rest of the world we are able to handle the situation well and we have dealt with all people appropriately and fairly, in an open and fair fashion."
The demonstrators are protesting against what they see as exploitation of the poor by the richer countries.
French anti-globalisation farmer Jose Bove defended the protests.
"What the small farmers want all over the world is to feed their own population," he said. "That's what the people are fighting for."