Taiwan’s military chief and seven others have died after a helicopter carrying high-level defense officials crash-landed Thursday morning in a mountainous region south of capital Taipei.

The Ministry of National Defense (MND) reported the casualties during an afternoon news conference. Taiwan’s chief of general staff, Shen Yi-ming, is among the dead. Five people survived the accident.

Taiwan’s official broadcaster Central News Agency also confirmed the death of Shen.

The 62-year-old took office as the top chief last year. He had earlier served as the 22nd Air Force commander of the Air Force and Deputy Minister of Defense, and has undergone military training in France and the U.S.

“I would like to extend my deepest condolences to the families of the victims,” Taiwan President Tsai Ing-wen wrote on Facebook. She added that Shen is an “outstanding general” and that his death is saddening.

The tragedy comes at a tense time for the self-ruled island, which is claimed by China. On Tuesday, the Taiwanese parliament passed an anti-infiltration law to combat perceived threats to the island’s democratic independence from mainland China as the island gears up for a presidential vote on Jan. 11.

The incumbent, Tsai, is running on the promise of upholding the territory’s sovereignty and maintaining a distance from the mainland. Beijing has said that it would not rule out using force against the island.

The Taiwanese UH-60M Black Hawk helicopter took off just before 8 a.m. and last made contact at 8:07 a.m., according to a defense ministry news conference. Taiwan air force commander-in-chief Hsiung Hou-chi said the helicopter went down in the hilly district of Wulai, and that the crash was caused by mechanical or environmental factors, which were yet to be clarified. Two rescue helicopters and 91 personnel were dispatched to the scene.

“Some of the people (on board) are still inside trapped, some have gotten out,” Hsiung said. “But as for the details, we still need the further report from the search and rescue team on the scene.”

The exact cause of the crash and conditions of the five who survived is not known.

According to the defense ministry, the helicopter was on a routine mission to visit soldiers stationed in Yilan, a county in the territory’s northeast, ahead of the Chinese New Year.

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Write to Hillary Leung at hillary.leung@time.com.