Rains hampered a military air operation to help flood victims in northeastern India, where more than two million people have been forced from their homes, officials said Wednesday.
Disaster management chiefs overseeing the aid effort in Assam state also said the number of people killed in flood-related incidents had reached 18 with five more casualties reported in the last 24 hours.
It is the third time this year that Assam has been hit by flooding.
Families stranded by the flood waters said they were close to starvation because the few aid packages that had been flown in were not enough to go round.
The defence ministry said heavy-lift helicopters were conducting up to 10 drops a day, each containing up to 1.5 tonnes of food, medicine and aid material.
But it admitted the relief operation was struggling because there was no let-up in the weather during what is the back-end of the monsoon season.
"Rains and strong river currents are hampering relief and rescue operations by soldiers and Indian Air Force helicopters," defence ministry spokesman S.S. Phogat said in Guwahati, Assam's largest city.
Phogat said he was unable to put a figure on the number of people rescued so far.
"Our priority right now is to rescue trapped people and reach food and medicines to those affected," he told AFP.
Mother-of-three Rupamoni Payeng said it was the third time this year she had fled to an elevated section of land on the submerged island of Majuli to escape flooding.
"We had to come here in June and August," she told AFP by phone, huddled inside a tarpaulin tent with the rest of her family.
She said the mood among other victims on the island, which is around 350 kilometres (220 miles) from Guwahati, was getting desperate.
A bulletin from Assam's disaster management department said the number forced to flee their homes had risen to two million, up by around 200,000 on the previous figure.
At least 19 of oil-rich Assam's 27 districts had been left under water, including 2,600 villages, it said. Some 400,000 hectares (988,400 acres) of crops were affected and 55 breaches of river banks had been recorded.
Assam's worst floods in recent years came in 2004 when 200 people were killed and five million people displaced.
Floodwaters have also submerged the 430-square-kilometre Kaziranga National Park, home to the world's largest concentration of one-horned rhinos. A 2012 census put the number there at 2,290, of a global population of 3,300.
Poachers took advantage of the chaos to kill one rhino, taking to 14 the number slaughtered this year. They also shot and wounded another, park wardens said.
The animals are killed for their horns, which fetch huge prices in Asian countries where they are deemed to have aphrodisiac qualities.
Flooding has also hit parts of neighbouring Bangladesh, where officials say nearly 250,000 people have been trapped by rising waters.
In Kurigram district, which borders Assam, more than 200,000 people have been trapped in their homes, district administrator Habibur Rahman told AFP.
"The flood situation is worsening, with the Brahmaputra River rising more than a foot (25 centimetres) in the last 24 hours. We've geared up relief for the flood-affected people," he said.