At around 5 a.m. on Jan. 10, on the sidewalk along Do Xuan Hop Street, Quach Hoang Kha, 24, lit a fire to warm himself while preparing to sell food. “After many years in Saigon, I have never felt it this cold,” he said.

Over the past three days, temperatures across southern Vietnam have dropped sharply, with many areas in Ho Chi Minh City recording lows of 17 C, the lowest in 10 years.