Taiwan's opposition and ruling parties are readying themselves for a showdown this week, amid growing calls for scandal-hit "president" Chen Shui-bian to step down.

The opposition plans to push for a referendum in the "parliament" to recall Chen over scandals involving members of his family.

The island's biggest opposition Kuomintang party (KMT) and its smaller ally People First Party (PFP) have agreed to seek a recall motion against Chen in the "Legislative Yuan."

"Lawmakers" are set to meet today to discuss whether to return from summer recess and hold an extraordinary "parliament" session, during which the opposition parties plan to initiate proceedings for the recall vote. A referendum on ousting Chen can only take place if two-thirds of Taiwan's 225-seat "parliament" approves the move.

The opposition would need the support of 10 independent "lawmakers" and another 25 from Chen's ruling Democratic Progressive Party (DPP) to achieve the required majority which is considered unlikely by analysts.

Ahead of a possible referendum to oust Chen, thousands of people took to the streets of Taiwan's capital city on Saturday, calling for his voluntary resignation for the second consecutive weekend.

Analysts say the protest was part of the opposition campaign to maintain pressure on Chen, whose approval rating has dived to record lows, and on investigators to press on with a probe into alleged financial wrongdoings.

Police estimated that more than 20,000 opposition supporters gathered in front of the "presidential" office building in Taipei, blowing air horns and waving yellow flags with the words "Down with A Bian," an abbreviation of Chen's name.

"We are not trying to usurp power. We are protesting against an incompetent and corrupt government," KMT Chairman Ma Ying-jeou told the PFP-organized rally.

"This may be a long struggle, but we have to hold out to the end and persist until we succeed."

Ma said there was no need to wait until there was evidence of illegal behaviour against Chen before launching a recall campaign.

"If a 'president' isn't fit to rule, you can recall him. He doesn't have to commit a criminal act," he said.

The KMT leader said Chen had lost the dignity necessary to function as "president." Chen "should resign to reduce the costs to society, so that people will at least still feel some sympathy and respect for him," Ma said. Ma cancelled a rally originally planned for the island's second-largest city, Kaohsiung, because of torrential rain.

"The pressure from these street protests is much greater than that of the recall motion as that vote can't pass," said Lu Ya-li, a professor of political science at the Chinese Culture University. "On the one hand, the protest puts pressure on Chen and on the other it puts pressure on the investigators," said Lu.

Editor: Yan