Indian authorities, hampered by heavy rain and damaged roads, were struggling on Saturday to get aid to millions of displaced villagers in the eastern state of Bihar, hit by the worst flooding in 50 years.

The Kosi river burst a dam in neighbouring Nepal earlier this month, deluging Bihar and drowning village after village in its path as authorities failed to evacuate millions in time.

About 85 people have been killed and more than 2 million displaced by floodwaters that have smashed houses and destroyed 100,000 hectares (247,000 acres) of farmland.

'Rains are killing our rescue and relief efforts,' Bihar disaster management department minister Nitish Mishra told Reuters.

'Our helicopters were barely able to fly for most of the day yesterday as it continued raining heavily till 4pm,' he said.

On Friday, an overcrowded army boat carrying dozens of flood victims overturned in the swollen river, drowning at least 20 people and leaving 10 unaccounted for.

Some 350,000 people have been evacuated over the past 10 days and thousands are marooned, said Pratyay Amrit, a Bihar disaster management official.

Army officers were putting up sandbags and wire mesh along roads in an attempt to fix embankments and prevent the swift flowing river from inundating new areas, said a Reuters witness in the flood-hit district of Saharsa.-Reuters