British Prime Minister David Cameron sent hundreds more troops into northern England on Sunday to help exhausted residents and emergency workers fight back rising river waters that have inundated towns and cities after weeks of heavy rain.

Cameron said the flooding is "unprecedented" and vowed to do everything possible to protect people and their property as the damage spread to the major cities York, Leeds and Manchester. He said protective systems and contingency plans will be reviewed because the frequency of such extreme weather events seems to be on the rise.

Weeks of persistent rainfall has saturated the ground and swollen the rivers to record levels, leaving entire swathes of northern England, and smaller parts of Wales and Scotland, vulnerable. Several hundred flood warnings remain in effect.

There have been no fatalities or serious injuries reported, but hundreds of people have been evacuated from houses and apartments in York, 200 miles (320 kilometers) north of London, where 3,500 properties are judged to be at risk. Emergency crews worked extra shifts to try to restore power to roughly 7,500 blacked out homes in the greater Manchester and Lancashire areas.

Environment Secretary Liz Truss said flood protection systems put in place in recent years were unable to cope with the record-high river levels.

"In Lancashire every single river was at a record-high," she said. "In Yorkshire we have seen some rivers a meter (yard) higher than they have ever been before. Clearly, in the light of that, we will be reviewing our flood defenses."

Several hundred peole had been evacuated the day before in the West Yorkshire and Lancashire regions and officials said thousands had lost power. The number of people affected continues to grow as flooding spreads and impacts cities as well as villages and towns.

A picturesque 200-year-old pub, The Waterside, in the greater Manchester area, collapsed and part of the structure was swept away by the River Irwell. Rising river levels also threatened downtown Manchester and police dealt with a ruptured gas main and small fire believed to have been caused by the flooding.

The Environment Agency urged residents to remain vigilant because more "severe" flooding is expected overnight and Monday.

The agency used its Twitter feed to beg people to be cautious, tweeting that driving or walking in flowing flood waters could be life-threatening.

Rescue crews have been using boats to help remove people from their homes and in some cases from their nearly submerged vehicles.