The BBC are reporting that arrests have now been made by the Met in West Yorkshire.
Six houses were searched and controlled explosions were carried out.
Police are looking for explosives in the raids (the first of which took place around 6:30 this morning) and "some materials" have been found already. No details on what that material is yet.
Up to 600 people have been evacuated from the area. Police cleared people from homes as well as a mosque, a health centre and an old people's home. Parts of the Beeston area of Leeds has been cordoned off, as well as a street in Dewsbury near the city.
No firm confirmation on how many arrests have been made or who the suspects are yet.