President Tsai Ing-wen cancelled campaigning to visit a radar station that Shen Yi-ming and his entourage were bound for on Thursday when their chopper smashed into mountains near Taipei.

The 62-year-old general was among eight killed in the crash, becoming Taiwan's highest-ranking military official to die on duty, while five people survived.

"I am finishing the mission for chief Shen to visit everyone on his behalf," Tsai told soldiers at the station in the northeastern region of Yilan.

"We are deeply saddened but the best way to honour Shen is to fulfil our duties and protect our country."

Investigators have recovered the Black Hawk helicopter's flight data recorder, which is being analysed to help determine the cause of the crash.

Tsai is seeking a second term in the January 11 elections against her main challenger Han Kuo-yu, with the debate dominated by relations with China.

In southern Tainan city, Han mourned victims of the crash at a campaign rally where his supporters dressed in dark clothes and held placards reading "rest in peace".

"We are really sad at this huge tragedy and we have to reflect and review the incident," he told the crowd after a moment of silence.

He also criticised Tsai's government over pension cuts, saying the move has shaken the faith of soldiers and public-sector workers.

Han, from the Beijing-friendly Kuomintang (KMT) party, had a stunning rise in 2018 local elections to become mayor of Kaohsiung city -- a traditional heartland of Tsai's Democratic Progressive Party (DPP) -- amid a backlash over government reform policies.

He has described January's vote as a choice between "peace or crisis" with China, campaigning on the slogan "Taiwan safe, people rich".

Taiwan has been a de facto sovereign nation since the end of a civil war in 1949, but China still views the island as its territory and has vowed to reunite it, by force if necessary.

Since Tsai's 2016 election, Beijing has sought to isolate the island because her party refuses to acknowledge Taiwan is part of "one China".

Tsai has described the election as a fight for Taiwan's freedom and democracy against an increasingly assertive Beijing.