Firefighters in France and Spain have slowed the spread of vast wildfires rampaging near Bordeaux and Madrid, officials in the two countries said, though they warned that the battle was far from over, with temperatures set to rise.

Officials in the Bordeaux region, where a fire has come within six miles of a factory that helps to build nuclear missiles, said on social media on Wednesday morning that the night had been “calm” and that several overnight flare-ups had been contained. Laurent Nuñez, the French interior minister, said on Tuesday night that two smaller fires elsewhere in southern France had been brought under control.

Spain’s prime minister, Pedro Sánchez, said on Wednesday morning that the battle against the fires around Madrid, the largest in modern Spanish history, continued to evolve “favorably.” He shared a mixed message of optimism and caution, saying that firefighters were dousing hot spots to prevent flare-ups as temperatures surged.

“The next 12 hours are going to be very important — decisive,” Mr. Sánchez said.

Spanish officials said that restrictions had been lifted for around half of the roughly 90,000 residents in the region who were ordered to evacuate or remain in place. But not all of the news was good. In eastern Spain, a separate fire near Valencia remained active overnight and had not been brought under control, officials said.

The office of Sophie Brocas, the prefect of the French region around Bordeaux, warned that temperatures on Wednesday could reach 41 degrees Celsius, or 106 Fahrenheit. Other “unfavorable” weather conditions were expected on Wednesday and Thursday, her office said, including high winds, falling humidity and a chance of thunderstorms, raising the prospect of lightning strikes that could cause a resurgence in the major fire.

“We remain on high alert,” Mr. Nuñez, the French interior minister, said on Tuesday night, echoing a similar message of caution from Prime Minister Pedro Sánchez of Spain earlier in the day.

The fires are the latest in a series of extreme weather events in Europe, the world’s fastest-heating continent, that scientists say have been made more likely by the burning of fossil fuels.

Record-breaking heat has led to parched vegetation that, combined with strong winds, has increased the risk of fires spreading. More than 300,000 acres have burned in Spain and France, prompting the largest peacetime evacuations in those countries.

Hari Raj contributed reporting.