LONDON, England (CNN) -- Nearly 150,000 homes were without drinking water Monday after the worst floodwaters in 60 years swamped large areas of western England.

About 50,000 homes are without electricity. Two major rivers -- the Thames and the Severn -- are already well above their normal levels and may burst their banks, according to authorities.

Britain's Environment Agency warned water levels could rise further to a "critical level" and issued nine severe flood warnings across the country.

The worst affected areas are the counties of Gloucestershire, Herefordshire, Worcestershire and Oxfordshire, which had more than 12.5 cm (5 inches) of rain in barely 24 hours.

More rain is forecast, and the risk of flooding is increasing as floodwaters work their way into the river system. Watch as Britons brace for more flooding ?

In the historic city of Gloucester, the River Severn is expected to burst its banks later Monday. The river is already nearly 5 meters (15 feet) above its normal level for this time of year and close to breaching its banks.

Electricity and water supplies in and around the city are already cut to many residents, after a water treatment plant and electricity sub-station were flooded. The city of Tewkesbury is also flooded -- video from the area showed dozens of cars and homes under several feet of water.

Hundreds of people in the worst affected areas have been plucked to safety by helicopters of the Royal Air Force and boats. Further north in Evesham, the River Severn is more than twice its normal width.

So far this month England has had nearly two-and-a-half-times its normal rainfall.

Prime Minister Gordon Brown visited Gloucester -- and promised to mobilize resources from across the country. He also announced increased funding for flood and coastal defenses across the country.

"Like every advanced industrialized country, we are coming to terms with the issues surrounding climate change," he said.

The prime minister described the flooding as unprecedented, and brushed aside criticism of his government for the quality of flood defenses and a slow response to the crisis.

"I think the emergency services have done a great job," he said. "I am satisfied people are doing everything they can."

The wet weather for much of June of July across England and Wales has also affected crops. Farmers are predicting low yields and higher prices -- with several crops due to be harvested in the next month. Insurance companies are expecting claims worth hundreds of millions of dollars because of flood damage.

More than 2,000 people spent Sunday night in emergency accommodation and the Royal Air Force and coastguard helicopters airlifted hundreds to safety in one of Britain's largest peacetime rescue operations.

"I'm afraid to say that I don't think we have seen the peak yet," John Harman, of the Environment Agency, told BBC radio.

"All this water that we have seen ... is now into the river system. Even though the rain has eased off a bit ... it's the water in the rivers now that constitutes a threat."