French nuclear giant Areva and Vinci engineering group subsidiary Satom admitted seven people including the wife of one of their employees were abducted on Thursday in the Arlit region some 800 kilometres northeast of the capital, Niamey.
Niger government spokesman Laouali Dan Dah said that the police and military have been called to find the seven, including five French nationals, a Togolese and a Malagasy.
There is no indication as to who abducted the seven Touareg rebels, armed bandits and the group Al-Qaeda in the Islamic Maghreb, AQIM, operate in the area.
The two firms say they have stepped up security for their remaining employees in Niger and are working with the authorities in both countries to secure the safe release of the hostages.
Last month France declared 'war' on AQIM after French hostage Michel Germaneau was murdered by the group.
France's huge nuclear power generating industry relies on Niger for 50 per cent of its fuel. Areva employs 2.500 people including many French expats mining uranium in the former African colony.