The Valais cantonal government said the fire danger was going to increase as temperatures climbed again following a brief respite from a weeklong heatwave that ended on Tuesday.
Record high temperatures, a lack of rain and strong winds are among the reasons cited by the government for the fire ban.
The cantons of Basel-City, Basel-Country, Solothurn and Vaud have already instituted similar fire bans.
“For many weeks, we have recorded only very little precipitation and the ground is very dry,” the Valais government said on its web page.
“Given this dryness and elevated temperatures, as well as the existing wind, people (are being asked) to follow strictly the directives of municipal authorities and all undertakings to preserve our forests, prairies, mountain homes (“mayens”) and residential areas against fires.”
The government said the situation could only be alleviated by a three-day spell of persistent rain.
“Rain of short duration and thunder storms will influence the current danger situation very little.”
The federal environment office said the fire danger in the canton of Valais was “very strong”, the highest level possible.
The cantons of Bern, Fribourg, Neuchâtel, Nidwalden, Zug, Graubünden and Jura have also called on residents to be prudent about fire risks.
Meanwhile, a small fire broke out on Thursday night in a wooded area above Arcegno in the canton of Ticino, the ATS news agency reported on Friday.
A dozen fire fighters from Locarno responded along with a helicopter to contain the blaze.
After all-time records for hot weather were set in many parts of western Switzerland during the heatwave, temperatures are set to head back over 30C on the weekend.
MeteoSwiss, the national weather office, is predicting highs on Saturday of 33C for Sion, the capital of Valais, and Basel, and 32C for Geneva.
No rain is expected anywhere in the country in the next six days, according to the office's forecast.