Flooding has hit dozens of towns in northern France, leaving roads sometimes only passable in boats and dozens of schools closed, authorities said Tuesday.

Two rivers -- the Aa and the Liane -- were placed on red alert for flooding in the northern Pas-de-Calais department after heavy showers overnight from Monday to Tuesday.

Interior Minister Gerald Darmanin said on X (formerly Twitter) that seven people were injured but did not provide further details. He said that more than 1,500 firefighters were mobilised in the region.

Coming on the heels of Storm Ciaran which battered Western Europe last week, the floods "impacted" around 60 municipalities, causing "significant" damage, said the prefecture, adding that dozens of schools have been closed.

Vigicrues, the official river flooding watchdog, described Tuesday's floods as "exceptional".

In the town of Blendecques, which was already hit by a flood last year, locals assessed the damage.

"Everything has to be repaired again," lamented Ludovic Provence, 43.

"We can't do anything against the water."

The red alert warning will remain in place until Wednesday evening.