Taiwan media are reporting that a helicopter of the same type crashed two years ago, killing six people.
While the official Central News Agency reported air force Gen. Shen Yi-ming had been rescued, citing rescue services, the defence ministry has not confirmed.
"Five have survived while the other eight of our colleagues on board were killed".
Taiwan's Ministry of Defense said in its statement that the crash site of the helicopter has been identified and two black hawks and about 80 military officers have been sent to the crash site. Shen was the top official of the General Staff Headquarters within the MND, responsible for command and control of Taiwan's military field units, and had been in the position since July.
The UH-60M Black Hawk military helicopter took off at 7:50 am (2350 GMT Wednesday) from Taiwan's capital Taipei City on a routine mission to visit troops in remote areas in eastern Yilan County.
"Today is a day that we are deeply saddened because several of our most distinguished generals died while on official duty", Tsai said at a briefing for the incident.
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"Most importantly, [we] must ensure the stability of our military and national defence."
President Tsai Ing-wen, who is seeking re-election, cancelled all campaign activities until Saturday, and urged authorities to make every effort at rescue. The ruling Democratic Progressive Party will also suspend campaigning for three days.
The incident, which comes a week before democratic Taiwan holds presidential and parliamentary elections on January 11, disrupted campaign events.
"We are investigating whether (the cause) was environmental or mechanical", he told reporters. Beijing has said that it would not rule out using force against the island.
The helicopter was heading for a military base in the island's northeast.