China's military has blasted a dam to release floodwaters threatening one of its most heavily populated provinces.

The operation in the city of Luoyang came after at least 12 people died in severe flooding in the Henan provincial capital of Zhengzhou, where residents were trapped in the subway system and left stranded at schools, apartments and offices.

Transport and working life have been disrupted throughout the province, with torrents of rain turning streets into rapidly flowing rivers, washing away cars and rising into people's homes.

More than 100,000 people have been evacuated to safety. Henan province is home to many cultural sites and a major base for industry and agriculture.

On Wednesday, state media showed waters at waist height, with rain still coming down.

To the north of Zhengzhou, the famed Shaolin Temple, known for its Buddhist monks' mastery of martial arts, was also badly hit.

China experiences regular flooding during the summer, but the growth of cities and conversion of farmland into subdivisions has raised the impact of such events.