The Jan. 13 election will shape Chinese-claimed Taiwan's relations with Beijing at a time China has stepped up military pressure to assert its sovereignty claims.

Vice President Lai Ching-te of the ruling Democratic Progressive Party (DPP), who China views as a separatist, leads opinion polls to be Taiwan's next president. Talks between the two main opposition parties to team up and take him on have floundered and are in deadlock.

Lai and his running mate, Taiwan's former U.S. envoy Hsiao Bi-khim, formally registered with the election commission on Tuesday to run in the election, but it remains unclear what the opposition will do. The deadline to register is Friday afternoon.

Lai told reporters he and Hsiao were "confident and determined to lead Taiwan steadily in the chaotic situation".

"Taiwan cannot afford chaos and experimentation at this moment," he said.

Only candidates with experience and ideas can successfully lead Taiwan to continue its steady progress, Lai said, standing with the DPP's lawmaker candidates for Taipei city.

Taiwan's main opposition party the Kuomintang (KMT), which traditional favours close ties with Beijing, had agreed with the much smaller Taiwan People's Party (TPP) last week to offer a joint ticket to take on Lai.

But neither party can agree how to interpret opinion polls on which of their candidates, the KMT's Hou Yu-ih and TPP's Ko Wen-je, should stand for president and which for vice president.

Hou on Tuesday called for re-opening talks on the opinion polls and said he had never insisted he had to be the presidential candidate.

The KMT's interpretation of the polls was that Hou being presidential candidate put him best placed to win over Lai and Hsiao, which the TPP has rejected as unscientific and not in line with its statistical analysis.

On Wednesday, Ko's campaign director Huang Shan-shan gave no sign of backing down and criticised what she said were attacks on her, the TPP and Ko by the KMT.

"Our enemy is Lai Ching-te. This turmoil has let Lai lie around at home. He's very happy," Huang said.

Ko, asked at a separate event what was going to happen, said: "There are still two days, don't be nervous".

Another presidential candidate is Terry Gou, the billionaire founder of major Apple supplier Foxconn who is standing as an independent but has also yet to formally register and has trailed in the polls.

His running mate, the actress Tammy Lai, briefly visited the election commission on Wednesday to pick up registration documents, but declined to say whether she and Gou, who did not accompany her, would actually register.

Bombarded by questions from reporters, Gou's campaign spokesman Huang Shih-hsiu would only say that "anything can happen" before the Friday deadline.

(Reporting by Ben Blanchard; Editing by Raju Gopalakrishnan)