The chief of the general staff, Shen Yi-ming, was among eight senior officers -- including three major generals -- who died when their Black Hawk helicopter smashed into mountains near Taipei.

The 62-year-old general and his entourage were on a routine mission to visit soldiers in northeast Yilan county when the incident happened.

"Five have survived while the other eight of our colleagues on board were killed. We are deeply saddened ... and give our condolences to their families," Air Force Commander Hsiung Hou-chi told reporters.

Survivor Tsao Ching-ping told rescuers in footage broadcast on local TV: "I am okay... two others are injured and only I can walk."

"There is one more person who's more seriously wounded and two or three people in the cabin ... while two more with no signs of life."

President Tsai Ing-wen's office said that she will cancel all campaign activities for three days after the tragedy. The ruling Democratic Progressive Party will also suspend campaigning for three days.

"As commander-in-chief President Tsai and the cabinet team will focus on the rescue operations as well as clarifying the cause of the incident," it said in a statement.

Tsai is seeking a second term against Kaohsiung city mayor Han Kuo-yu of the Kuomintang (KMT) party in the January 11 elections when Taiwan will also elect a new parliament.

Han -- who will stop campaigning for two days -- and the KMT also expressed condolences to the victims.

There have been a number of incidents involving Black Hawk helicopters -- purchased from the United States -- in recent years in Taiwan.

In 2018, a chopper belonging to a government rescue agency crashed during a medical mission off outlying Orchid Island, killing six people on board.

There were also two crash landings in 2016 and 2018 with no casualties.

The chopper carrying 13 people disappeared from radar less than 15 minutes after taking off, according to Hsiung, adding that the ministry had set up a taskforce to investigate the incident.

"We are investigating whether (the cause) was environmental or mechanical," he said.

An air force official said some on board were "trapped under fragments of the helicopter" without elaborating.

The ministry has dispatched ground troops and rescue helicopters to the crash site in northeastern Taiwan.

"It had been raining in the mountains in the past few days, the mountain roads are muddy and very steep. We are racing against time," Chen Chung-chi, a supervisor of the operation, said earlier Thursday.