Arroyo's aides linked former president Joseph Estrada and several others to the plot. Estrada laughed off the allegations, saying that he's been out of work and under detention for five years and didn't have the money to finance a coup.
"I don't have any work, how can I finance?" he asked.
Aquino, a one-time Arroyo ally, criticized the emergency declaration and reiterated a call for Arroyo to "make the supreme sacrifice" and resign.
"I believe that during these times, we should not forget that many sacrificed to regain our democracy," Aquino said. "We cannot just keep quiet because that is what happened during martial law. Our dictator then believed that he can do anything to keep himself in power."
The opposition said the declaration showed the government's desperation.
The Integrated Bar of the Philippines, the largest lawyers' group in the country, said it would question the legality of Arroyo's declaration before the Supreme Court, according to its president, Anselmo Cadiz.
"It could result in more political hemorrhage and security risk," said Representative Roilo Golez, Arroyo's former national security adviser, who withdrew support from her. "This could get out of control ... if her crisis team doesn't manage this well."
Representative Teodoro Casino, a leftist leader, said anti-Arroyo protests won't end.
Military chiefs said they backed Arroyo. They arrested an unspecified number of people, including an army general who leads an elite special forces unit, for alleged involvement in a coup plot.
"We have reduced the threat," army chief of staff General Generoso Senga said. "We cannot say that it has been stopped."
Additional reporting by Chang Yun-ping
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