Pakistan has dispatched medical teams to the northwest amid fears that cholera could spread in the aftermath of the worst floods in the country's history.

The disaster has already killed up to 1,200 people and forced another 2 million to flee their homes. Thousands more people in Khyber-Pakhtoonkhwa province remain trapped by the floodwaters.

Many residents of Pakistan's northwest waded through the flood water to dry land - some to makeshift shelters, others to their damaged houses to salvage their remaining possessions.

Now people in the northwest also face the threat of waterborne disease, which could kill thousands more if health workers cannot deliver enough clean drinking water and treat and isolate any patients in crowded relief camps.

Officials have yet to receive concrete reports of cholera cases, but fear of an outbreak is high, according to the top medical official in Khyber-Pakhtoonkhwa. Patients with stomach problems from dirty water are being treated in government medical camps.

The Queen sent a message of condolence to Pakistan's President Asif Ali Zardari, saying: "I am deeply saddened at the tragic loss of life and suffering that Pakistan has been experiencing as a result of the ongoing monsoon floods. I offer my heartfelt condolences to the families and friends of those who have been killed, and my deep sympathy to all whose lives have been affected."