Firefighters are combating a major wildfire in nature reserve De Peel in Limburg, with locals told to close windows and doors to keep out the smoke, local media report.

The blaze, which had consumed 20 hectares by the end of Wednesday morning, is not yet under control, because access to the area is difficult,  a fire brigade spokesman told local broadcaster Limburg 1.

The fire was reported by birdwatchers at 6.30am. It is too early to say how it originated, a safety region official said. ‘It could be any of a number of things. Fires don’t make themselves but the exact cause is unknown.’

Two years ago a nearby area was struck by a fire which went underground and took months to put out. Some 800 hectares of heath land were destroyed at the time.

That is not a risk this time, the official said, because the underlying soil is not as dry.

The fire brigade said it will probably take all day to put the fire out and has asked people to stay away from the area and keep roads free for emergency services.