A KMT official said on condition of anonymity that the fight was inevitable, as Ma was unlikely to appoint or hand-pick a future successor. 'Given his insistence that everything must go by the rules, the president is not likely to choose his own successor,' the official said. 'So the aspirants must rely on themselves to win the nomination.'

Wu, 64, is a veteran politician who was a legislator before serving as a two-term mayor in both Nantou in central Taiwan and then Kaohsiung in the south.

'Being Ma's deputy ... Wu stands a big chance of winning the party's nomination,' said political analyst Niu Tse-hsuan, a professor of public affairs at the Chinese Culture University in Taipei. 'Chu is equally competitive, given his much-approved administrative performance as head of Taoyuan and Xinbei, whose populations make up one-fourth of Taiwan's population,' Niu said.

The 50-year-old Chu is a financial expert who was educated in the US and served as vice-premier when Ma won his first presidential term in 2008. A year later, Ma asked Chu to seek the Xinbei mayorship. Chu captured the post by beating Tsai Ing-wen, the outgoing chairwoman of the pro-independence Democratic Progressive Party who was defeated in Saturday's presidential election.

Local media said Taipei Mayor Hau Lung-bin could be a dark horse for the presidency, given his defeat of Su Tseng-chang, premier in the government of former president Chen Shui-ban, by more than 170,000 votes in 2010 to secure a second term. Another wild card is Interior Minister Jiang, known for his high job-approval rating and his clean image.

Meanwhile, Annie Lee, daughter of former president Lee Teng-hui, suggested that first lady Christine Chou Mei-ching run for president in 2016, given her popularity on the island.

But regardless of who wins the KMT nomination, pundits expect the candidate to face a fierce battle - likely more difficult than that which Ma encountered in his recent campaign - if Tsai stages a comeback to run for president in 2016.

Tsai, 55, a former vice-premier under Chen, was Ma's top challenger in January's election, running neck and neck with him for much of the campaign before Ma won by six percentage points.

'Tsai has slowly built up her political clout through her rational approach to help the DPP change its image from radical to moderate so it is able to once again stand firm on its feet,' said political commentator Shen Fu-hsiung. The DPP suffered a major setback after its image was badly tainted by a string of corruption scandals that led to the jailing of Chen in 2009.

'If Tsai Ing-wen stages a comeback in 2016, given her moderate image and her political clout, whomever faces her from the KMT will have an even tougher battle than in the recent election,' Shen said.

The soft-spoken Tsai reversed the DPP's traditional approach of resorting to sensation and confrontation during her run for the Xinbei mayorship in 2010. Her moderate approach won support from a great number of neutral voters, and she was gradually accepted by DPP supporters.

In her concession speech, she did not shift the blame to the KMT for her failure but asked the party to review itself in order to progress.

Tsai has said she will not shy away from politics and intends to set up an office to continue her political work. 'We should not give up something that took us so much to build,' she said, adding that it was the responsibility of the DPP not to let society down.