Local media reported a truck fell from a cliff in eastern Taiwan and landed on a train line, where a passenger train emerging from a tunnel smashed into it.
The train was carrying around 350 people, and rescue efforts are ongoing, the fire department said.
With much of the train still trapped in the tunnel, escaping passengers were forced to scale doors, windows and roofs to reach safety.
Taiwan's President Tsai Ing-wen said a number of people are trapped, according to the BBC.
More than 72 people were injured, with around 60 already sent to hospital.
CNA said a truck that was "not parked properly" was suspected of sliding into the path of the train.
"Around four people are without life signs", the Central Emergency Operation Center said in a statement, adding rescuers were trying to get to four carriages inside the tunnel that were badly damaged and hard to access.
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"Our train crashed into a truck", one man said in a video aired on Taiwanese television, showing pictures of the wreckage.
The fire department showed a picture of what appeared to be the truck's wreckage lying next to the derailed train, and an aerial image of the end of the train sitting on the track next to a construction site.
The accident came on the first day of the four-day Tomb Sweeping Festival, an annual religious festival when people travel to their hometowns for family gatherings and to worship at the graves of their ancestors.
The line connecting Taipei with Hualien was only opened in 1979.
In 2018, a passenger train with 366 passengers on board derailed in Taiwan's Yilan County, claiming 18 lives and wounding over 160.
Taiwan's Eastern Railway is a popular tourist destination because of its spectacular coastline and scenery.
That crash was the island's worst since 1991, when 30 passengers were killed and 112 injured after two trains collided in Miaoli.