GONDOMIL, Portugal (Reuters) - Hundreds of Portuguese firefighters struggled on Wednesday to contain wildfires which erupted far earlier in the season than usual because of unexpectedly hot and windy weather.

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Ten fires were burning across the country, most in the north, several months before the late spring season when fire crews are normally in place. Meteorologists said global warming had made it difficult to predict where blazes would erupt.

“We are having significant fire outbreaks in areas where we didn’t know the risk was high,” Miguel Miranda, president of the Portuguese Institute of Meteorology (IPMA), told Portuguese radio station TSF. “We are in unexplored territory, we have never been through this.”

Helicopters dropped water on flaming woodlands near the tiny village of Gondomil on Portugal’s northern edge near the Spanish frontier. A firefighter there told Reuters the force was waiting at a wooded area until the weather conditions made it possible to fight the blaze.

There were no immediate reports of casualties or figures for property damage. Portugal’s government issued a wildfire alert on Tuesday evening, with no rain in sight and temperatures at the start of the week that soared as high as 28 degrees Celsius (82 Fahrenheit), far above seasonal norms.

The weather conditions resemble those that caused a devastating wildfire in the central town of Pedrogao Grande in June 2017, killing 64 people and injuring more than 250, the worst disaster in modern Portuguese history.

The government warning prohibits farmers from using slash-and-burn methods and requires employers to authorise absences for workers who serve as volunteer firefighters.

Temperatures are expected to remain unseasonably hot, according to IPMA, with the temperature in the northern river city of Porto expected to reach 24C on Wednesday, compared with a March average of 12C.

“This meteorological scenario means an increase in the fire risk index from Monday until Wednesday with favourable conditions for the rapid spread of fires throughout the mainland, with high to very high levels,” the Civil Protection agency said on its website.

The most aggressive wildfire raged in the municipality of Oliveira de Azemeis since the early hours of Tuesday morning, with 450 firefighters on the ground who managed to bring it under control on Tuesday.

In the district of Esposende, also in northern Portugal, a wildfire on Tuesday forced authorities to evacuate two schools due to high levels of smoke. It has since been put out.