Taiwan's two main opposition parties have agreed to unify their candidates for the upcoming Taiwan's presidential election in January.

The largest opposition Kuomintang Party has picked the mayor of New Taipei City, Hou Yu-ih, as its candidate. The second-largest opposition Taiwan People's Party, which is the third-largest group in the legislature, has put forward former Taipei Mayor Ko Wen-je.

The two opposition parties reportedly agreed on Wednesday that either Hou or Ko will run as a candidate for president, while the other will be a vice presidential candidate.

Party officials say their joint presidential candidate will be announced on Saturday after experts analyze various public opinion polls.

The ruling Democratic Progressive Party has chosen Taiwan Vice President Lai Ching-te to compete in the presidential race.

Hon Hai Precision Industry founder Terry Gou has also qualified to run as an independent candidate.

Opinion polls have indicated Lai as the frontrunner, with Hou and Ko competing for second place.

Opposition party members and their supporters had called for a unified candidate to improve the prospects of a change of government, particularly as registration of candidates is set to start on Monday.