Syrian President Bashar Al Assad declared a national catastrophe on Tuesday after inspecting crops destroyed by wildfires that have ravaged his country's Mediterranean coastal belt.

As many as 25,000 people have been forced to flee their homes, the United Nations said, in a new blow for a region which is a mainstay of support for Assad's government.

The fires, which broke out in tinder-dry conditions on Friday, have destroyed more than 9,000 hectares of farmland and forest in the coastal provinces of Latakia and Tartus, as well as Homs inland.

In the hardest hit province of Latakia, three people died and at least 70 were admitted to hospitals, the UN humanitarian affairs office said.

Assad pledged support for residents of affected areas, especially farmers who have lost their crops.

"This is a national catastrophe... humanitarian, economic and environmental," Assad said.

"The state will bear the largest burden in offering this support," he said.

Wildfires are a regular occurrence in Syria in late summer, as they are in neighbouring Israel, Lebanon and Cyprus.

But this week's fires have been on a larger scale than usual, residents say.