PHNOM PENH, Cambodia (AP) — Cambodian authorities have ordered a one-hour reduction in the length of school days because of concerns that students and teachers may fall ill from a prolonged heat wave.

Education Minister Hang Chuon Naron said in an announcement seen Friday that the shortened hours will remain in effect until the rainy season starts, which usually occurs in May. The current heat wave, in which temperatures are regularly reaching as high as 41 Celsius (106 Fahrenheit), is one of the longest in memory.

Most schools in Cambodia lack air conditioning, prompting concern that temperatures inside classrooms could rise to unhealthy levels.

School authorities were instructed to watch for symptoms of heat stroke and urge pupils to drink more water.

The new hours cut 30 minutes off the beginning of the school day and 30 minutes off the end.

School authorities instituted a similar measure in 2016.