Twnety-six others were injured in the blast on the 12th floor of the Shin Kong Mitsukoshi department store in the central city of Taichung, the fire department said.
The blast on the building's 12th storey, where construction work was taking place, caused damage from the ninth floor upwards, the fire department said.
Speaking from the scene, Taichung mayor Lu Shiow-yen said the shock of the blast was felt at her office nearby.
She said the fire bureau would focus on a rescue operation first but an investigation was also under way.
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