PESHAWAR, Pakistan — Flash floods triggered by torrential rains Sunday killed at least 45 people in northwest Pakistan, officials said.

Rains started overnight Saturday and caused flash flooding in several districts of Khyber Pakhtunkhwa province, said a Pakistani national disaster management official, Latif ur Rehman.

Another 34 people were admitted to hospitals with injuries, he said.

Flash floods are commonly triggered during South Asia’s summer monsoon season. Premonsoon rains like the current downpour frequently cause damage in Pakistan — particularly in rural villages with minimal infrastructure.

Residents of scores of villages close to rivers were given warnings to vacate and leave for safer places, Rehman said.

‘‘We’re left on our own. Nobody from the government is coming to help us,’’ said Habib Khan, a resident of the northern Swat valley, talking to a local TV news channel.

The channel showed damaged houses and submerged streets in the valley and other parts of the northwestern province.

In parts of Southeast Asia, countries are enduring their worst drought in 20 or more years. Tens of millions of people in the region are affected by the low level of the Mekong, a rice-bowl-sustaining river system that flows into Laos, Thailand, Cambodia, and Vietnam.

Fresh water is running short for hundreds of thousands of people in Vietnam and Cambodia, and reduced water for irrigation has hurt agriculture, particularly rice growing in Thailand, where land under cultivation is being cut significantly this year.

Vietnam estimates that 1,500 square miles have been affected by saltwater intrusion, with some 640 square miles rendered infertile. The affected land accounts for nearly 10 percent of the country’s paddy cultivation area in the Mekong Delta, its main rice-growing region.

Associated Press