A severe rainstorm swept through parts of southern Nepal late on Sunday, killing at least 27 people and injuring nearly 400, Ministry of Home spokesperson RK Subedi told All India Radio. Twenty-six people were killed in Bara district while one died in Parsa.

“Helicopters have been kept ready for immediate rescue and relief,” Prime Minister KP Oli said on Twitter, adding that security forces have been alerted. The rescue teams were waiting for the weather to clear to help the injured people in affected villages, the Nepali prime minister said.

The thunderstorm has hit many villages in Bara and Parsa districts, reports said. Bara, located nearly 128 km south of Kathmandu, borders Bihar.

At least 24 people were killed in Bara district, and one person died in Parsa district, PTI quoted unidentified Nepali home ministry officials as saying. The number of deaths was likely to increase as rescuers were still trying to reach many of those affected, Rajesh Poudel, a bureaucrat of Bara district, told Reuters.

Poudel said most of the deaths and injuries were caused by falling objects and collapsing huts and trees, AP reported.

Prime Minister’s Chief Adviser Bishnu Rimal said army personnel have been mobilised. “Two battalions have been mobilised immediately there, here in Mid Air Base, Kathmandu; night vision helicopters are on stand by with rescue team,” Rimal told The Himalayan Times. “Our security agencies are waiting for favourable weather conditions [sic].”

Nepal’s National Emergency Operation Centre said the injured were being treated at various health facilities, PTI reported. The injured were brought to a hospital in cars and ambulances, but roads in many villages were blocked due to fallen trees and electricity poles.