Shots have been fired and petrol bombs thrown in the Creggan area of Derry.
The Police Service of Northern Ireland said one person had been taken to hospital and appealed for calm in the area.
Images shared on social media showed a fire burning in a van and a car as people looked on, while another video showed a firework exploding underneath a police van.
A police cordon is now thought to be in place in the area and Army Technical Officers are also said to be at the scene.
A house in Mulroy Gardens was reportedly being searched.