"The fire is spreading towards Ried-Morel-Riederhorn," police said in a brief statement on Twitter at 18:30 GMT, saying they would evacuate the Ried-Morel village, near the town of Brig, which is close to the Italian border, according to Reuters.
It later added that three other villages were to be evacuated and warned of rockfalls.
Air Zermatt, which operates four of the helicopters, said efforts to extinguish the fire would continue through the night. Valais police posted pictures showing a helicopter dangling a water cannon above a forest fire in the afternoon.
A later shot showed a much larger fire with smoke eclipsing most of the forest.
The area is affected by the same Mediterranean heatwave affecting southern Europe, with temperatures set to exceed 30 Celsius in parts of the Valais canton this week, forecasts show.
RHM/PR