The train, which was traveling to Taitung, came off the rails in a tunnel at around 9:00 a.m. local time, causing some carriages to hit the walls, the fire department said.
The train was carrying around 350 people, and rescue efforts are ongoing, the department said.
The crash, which also injured more than 40 passengers, is the island's worst rail disaster in at least four decades.
Another live broadcast by UDN outside the tunnel showed at least two undamaged train carriages with rescuers helping passengers escape.
Taiwan's President Tsai Ing-wen said a number of people are trapped, according to the BBC.
More than 40 people have already been taken to hospital and others injured are in the process of being taken to hospital, with around 70 reported trapped in train carriages.
Television footage and photos posted by people at the scene on the website of the official Central News Agency showed people climbing out the open door of a railcar just outside the entrance to the tunnel.
Breaking: A train derailed in the east # Taiwan Earlier today, and step Oc Focus_Taiwan, Many showed no sign of life. "The truck came falling down".
In 1981, 30 were killed in a collision in northern Taiwan, and in 1991 another 30 died in a train crash.
Reports said a truck fell from a cliff above and landed on the tracks, where a train emerging from a tunnel smashed into it.
Taiwan's eastern railway line is usually a popular tourist draw down its dramatic and less populated eastern coastline.
The accident occurred at the start of a long weekend for the traditional Tomb Sweeping Day hospital.
In 2018, a passenger train with 366 passengers on board derailed in Taiwan's Yilan County, claiming 18 lives and wounding over 160.