More than 550 people have been killed in flooding caused by heavy rains across northern India, Nepal and Bangladesh.

Annual monsoon rains have triggered landslides and caused homes to collapse, and with many more people dying due to drowning, the death toll stands at 578.

Almost 16 million people are thought to have been affected by the flooding, with army soldiers and disaster management workers across the three countries launching mammoth rescue efforts to evacuate and provide food and shelter to those caught up in the disaster.

Soldiers have been forced to use motorboats to rescue people marooned on their rooftops, while air force helicopters dropped packages of food and drinking water to those trapped in their homes.

People affected by the flooding sleep at the roadside after being forced to leave their homes. Credit: AP

In the northern Indian state of Bihar, 11 million people have been affected by the flooding, with almost 500,000 in 1,300 in state-run relief camps where they are being provided with food and medical care.

More than 225 animals are also thought to have been killed in the famous Kaziranga National Park which has been almost entirely submerged in water.

Around 15 rhinos, a Royal Bengal tiger, and 185 deer were among the animals killed.

Hundreds of other animals were forced to flee the park in Assam state.

The monsoon season lasts from June until September.