UPDATED 11.23am: Armed men who have taken hostages in the northern French town of Roubaix appear to have no link to the November 13 attacks by Islamist militants in Paris but were probably planning a robbery, police sources say.

"This is apparently not a terrorist attack, it's apparently a robbery," one police source said on Tuesday.

It is understood a bank director and his family may have been taken as hostages.

Medical and fire services confirmed that an operation was underway in Roubaix, which is near the border with Belgium, without giving further details.

France remains on high alert after the attacks in and around Paris in which 130 people were killed.