Continuing downpours of torrential rains in Pakistan have frustrated the efforts of relief workers trying to reach those affected by the country's worst floods in 80 years.

Government and humanitarian workers have had the monumental task of assisting some 3 million people affected by the harsh weather, many of whom have been displaced and are without food.

"Thousands of people are still waiting to receive assistance. It is crucial to get humanitarian aid to the people and the places that need it most," said Robin Greenwood of UK-based relief agency Christian Aid.

"There is an acute need for food, kitchen utensils, mosquito nets and tents," says Emmeline Managbanag, vice president of Church World Service Pakistan, which has mobile health units providing basic services.

Along with the rain, massive destruction of bridges and roads throughout the country has made relief efforts difficult.

Zia Nawab of Action Aid said that the destruction is "vast: whole villages and settlements have been washed away, the entire geography of the area has been altered."

"Access to most affected areas is difficult as roads and bridges have been damaged. With more heavy rain, rivers could burst their banks - the situation is now at tipping point," he added.

Death tolls have risen to over 1,500 since the deluge began last week, and swathes of crops and livestock have been killed.

Concerns about water-borne diseases are high but reaching those who have been isolated by the floods is currently top priority.

The United States government has issued $10 million in emergency relief aid as President Barack Obama sent his condolences to those affected.

"The President recognizes the importance of allies helping allies in times of need," a spokesman for President Obama said on Tuesday.

"Our relationship with Pakistan goes far beyond our shared commitment to fight extremists. The United States government stands ready to continue to assist Pakistani authorities address the difficult challenges posed by this natural disaster," he added.