French officials urged caution Thursday as a record pre-summer heatwave spread across the country from Spain, where authorities were fighting forest fires on a sixth day of sweltering temperatures. The Meteo France weather service said it was the earliest hot spell ever to hit the country, worsening a drought caused by an unusually dry winter and spring, and raising the risk of wildfires. Spain, which has already seen its hottest May since the beginning of this century, was sweating under temperatures forecast as high as 43 degrees Celsius (109 Fahrenheit) and no relief is expected before Sunday, the Aemet weather service said. At least three forest fires erupted in Catalonia, including one near Baldomar around 140 kilometres (87 miles) northeast of Barcelona, that has burned nearly 1,000 hectares (2,470 acres) but could grow to 20,000 hectares before it is contained, the regional government said. No evacuations have yet been ordered but people are being urged to remain in their homes. Neighbouring Portugal saw its hottest May since 1931, with most scientists attributing the early season heat across Europe to global warming caused by greenhouse gas emissions.