The Puyuma express train was carrying more than 360 passengers to Taitung city when it derailed at 4.50pm local time in the rural township of Tungshan, the transportation ministry's railway administration said.
Most of the victims died on the train while others succumbed to their injuries in hospital, he said.
Taiwan's Central News Agency reports that dozens may still be trapped.
Images from the site showed the high-speed Puyuma Express train completely derailed and lying zig-zagged across the track. Five of the cars are turned over on their sides.
Soldiers have been removing bodies to identify them, he added, but nightfall was complicating rescue work.More news: Canada becomes second country to legalize marijuana nationwide
Passengers were trying to escape through train windows and that bystanders had gathered to help them before rescuers arrived, local media reports said. However, one of them was later identified by the Ministry of Foreign Affairs as a 43-year-old US citizen, a female who was admitted to St. Mary's Hospital Luodong. A total of 17 people were declared dead before being sent to hospital.
The wreck happened at a railway station called Hsin Ma, but the train was not scheduled to stop there.
The Puyuma was launched in 2013 to handle the very hard topography of Taiwan's east coast and is distinct from the high-speed rail that runs on the west coast. It is distinct from the high-speed rail that runs on the west coast. In 2003, a train traveling toward a mountain tourist destination crashed, killing 17 passengers and injuring another 156, and a toppled tree caused a train crash that killed six and injured at least 50 in 2011. Five people were killed and 16 others hurt.
In March this year, a carriage of a train on its way to Taipei derailed inside Shulin station in New Taipei City. Investigators blamed brake failure.