Clashes have broken out between Hong Kong's pro-democracy protesters and police after the protesters attempted to bring in loudspeakers and other audio equipment to the campaign area.
The authorities have deployed about 200 policemen following the clashes as the situation remains tense.
One of the Occupy Central organisers, Chan Kin-man, urged the campaigners to maintain calm.
"In case of conflicts, please raise both of your hands to show that you have no intention to attack law enforcement officers," Chan told the gathering.
Local reports say the protesters are equipped with goggles and umbrellas to protect themselves from pepper spray.
The protesters, who have launched a civil disobedience movement in the city state, have demanded that China withdraw its proposal to undertake political reforms in the former British colony.
The demonstrators also want more public participation in the politics of the semi-autonomous Hong Kong.
"We demand [Hong Kong chief executive] CY Leung deliver a new report on political reform to the central government, which must adequately reflect the demands of Hong Kong people for democracy. If CY Leung does not respond, we will escalate our actions," a statement from Occupy Central said.
In a rare show of strength, thousands of students and others gathered to take part in the protests demanding democratic reforms.
Police have arrested scores of protesters, including key student leaders, in the past several hours.
According to reports, there was some disagreement between the student protesters and the Occupy Central demonstrators shortly after the Occupy campaign took over the protest venue.