LANZHOU - Twenty-one people have died and four are missing after rainstorm-triggered floods and mud-rock flows hit a city in Northwest China's Gansu province, the local government said on Saturday.

Four rounds of downpours, which swept Tianshui city recently, triggered floods, landslides and mud-rock flows in seven townships and left people missing and buried, said the Tianshui city government.

Rescuers work to save people after downpours hit Niangniangba township, Gansu province, July 26, 2013.

Nine out of 28 villages in Niangniangba township in Qinzhou district remain isolated because power, communications and roads were cut off, said the government.

In Rongguang village of Niangniangba, more than half of the houses were destroyed in the natural disasters, said a rescuer.

The local government have dispatched nine squads to these villages to check the damage there. Firefighting departments in Tianshui also sent 50 rescuers to the areas.

More than 1.2 million residents in seven counties and districts were affected by the rainstorms, with 30,000 evacuated.

The Tianshui municipal government said helicopters, excavators, generators, medicine and food, tents and quilts were needed for relief efforts.

The local meteorological station forecast the city would have a new round of heavy rain in the next few days.