LONDON - Prime Minister David Cameron said on Wednesday “a fight back is under way” to restore law and order to Britain's streets but rioting, looting and arson by gangs of youths spread from London to other cities overnight. Youths fought running battles with police in the northern cities of Manchester and Liverpool as well as in the Midlands. They smashed shop windows, carted off televisions and designer clothes, and torched buildings as police armed with shields and batons struggled to maintain control. A boosted police presence meant London itself was relatively quiet after three days of violent unrest that shocked the nation and raised questions about the divided state of modern Britain. About 16,000 police officers patrolled London's streets on Tuesday night but with shops, pubs and businesses in many areas closing early and boarding up windows, the city which hosts the Olympic games next summer, had the air of a town under siege. “We needed a fight back and a fight back is under way,” Cameron said after a meeting on Wednesday of the government's COBRA committee that deals with national security crises. “Whatever resources police need they will get.” This included baton rounds and water cannon, Cameron said. The prime minister branded the unrest, which erupted in poor, inner-city areas of London at the weekend, as nothing more than criminality and made no reference to social and economic conditions which community leaders say sparked the problems. “There are pockets of our society that are not just broken but frankly sick,” said Cameron, who made fixing “broken Britain” a cornerstone of his premiership. But the spread of the unrest to other cities including Birmingham, Britain's second biggest, means the crisis is anything but over. Gangs of youths in hooded tops battled police in Manchester, smashing windows and looting shops, and setting fire to a clothes shop. In nearby Salford, rioters threw bricks at police and set fire to buildings. TV pictures showed flames leaping from shops and cars, and plumes of black smoke billowing across roads. “These people have nothing to protest against — there is no sense of injustice or any spark that has led to this,” Assistant Chief Constable Gary Shewan said. “It is, pure and simple, acts of criminal behaviour which are the worst I have seen on this scale.” I n Liverpool's Toxteth district, rioters attacked two fire engines and a fire officer's car, police said. Earlier, some 200 youths throwing missiles wrecked and looted shops.