More than two dozen people have been killed in a severe thunderstorm that swept through parts of southern Nepal and hundreds more were injured, police and officials said.

Nepal’s prime minister KP Sharma Oli wrote in a tweet that 25 people had been killed on Sunday, and around 400 were injured.

“Helicopters have been kept ready for immediate rescue and relief,” Oli said. He offered condolences to the families of the victims.

Rajesh Paudel, government administrator of Bara district where the storm hit, said the death toll may increase as rescuers were still trying to reach many of those affected.

Bara is located about 39 miles (62km) south of Kathmandu, and borders India’s eastern state of Bihar.

Pre-monsoon thunderstorms are common in Nepal during the spring season, but are rarely of an intensity that causes high casualties.

Police superintendent Sanu Ram Bhattarai said rescue teams had been dispatched to the affected villages, but reaching the victims was difficult at night.

Television channels said the storm and accompanying heavy rainfall, uprooted trees and electric and telephone poles, crushing some people to death.