State radio said on Sunday the National Security Service (NSS) and police had arrested 185 people after protests Friday against Gayoom, Asia's longest-serving leader.
But the Moldavian Democratic Party (MDP), which is campaigning for a multi-party democracy in the tiny, one-party Indian Ocean atoll nation, said hundreds more were detained Sunday.
"Our activists are in hiding," MDP spokesman in Colombo, Mohamed Latheef, told AFP. "Security personnel are going from house to house and pulling out suspected dissidents and beating them up in public."
The MDP called on the international community to take action to prevent the country of 270,000 Sunni Muslims from slipping into chaos after a state of emergency was imposed Saturday.
Among those detained was Ibrahim Zaki, the former secretary general of the seven-member South Asian Association for Regional Cooperation (SAARC) and the former Maldives attorney general, Mohammed Munavvar, government officials said.
Residents said streets in the one-mile (1.6-kilometre) long island capital were calm Sunday, with shops open and the government ordering civil offices and schools to function normally.
They also said there was no disruption to tourism, the archipelago's main foreign exchange earner.
Holidaymakers who visit the Maldives are usually ferried from the airport island to resorts by boat or seaplane without having to go through the capital island of Male.
In the highly congested capital, home to 80,000 people, Gayoom's sea-front palace was tightly guarded with two heavy military vehicles parked across the main road to prevent cars entering the area.
Authorities cut off Internet access and short message services (SMS) on mobile phones to prevent pro-democracy activists from contacting people outside. However, Gayoom's official website was being regularly updated.
Telephones were operating but residents said they feared phones were tapped.
Gayoom has ruled the Maldives since 1978, turning the once fishing nation of 1,192 coral islands into a prosperous upscale tourist spot.
But he has faced mounting criticism at home and abroad for failing to tolerate any opposition. He began cautious reforms after an unprecedented riot in Male last September triggered by the death of an inmate at a nearby prison.
Dozens were hospitalized Friday when police fired teargas and used sticks and batons to break up a protest calling for release of political prisoners.
The president said security services used "minimal force" to disperse the mob and the main instigators of violence had been arrested.
In an address to his cabinet, Gayoom said those detained would face trial and "praised members of the NSS and the police for the courage they displayed in restoring peace and calm in Male" his website reported.
"Members of the cabinet noted the measures that the president had taken to control the situation reflected patience, wisdom and leadership, and that they fully supported these measures."
Gayoom's office said police tried to "restrain" the demonstrators for 17 hours but protestors torched a government building and stabbed two unarmed policemen.
Regional power India said it was "naturally concerned" about the situation.
"We are watching the developments," foreign ministry spokesman Navtej Sarna said in New Delhi.
Amnesty International appealed to the Maldives to abide by human rights in looking after detainees.
