PATNA, India (Reuters) - Indian authorities, hampered by heavy rain and damaged roads, were struggling on Saturday to get aid to millions of displaced villagers in 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 4 p.m.," 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.

The witness also saw more than 1,000 people from nearby villages walking to the city, where they hoped to find food and shelter. Some villagers who chose to stay, built temporary bamboo shelters on high ground, eating uncooked rice and flour mixed with polluted water.

"We keep sitting here the whole night and wondering what to do. How will life go on? Will we survive or not?" said Virender Kumar Saga.

Floods have killed more than 1,000 people in South Asia since the monsoon began in June, mainly in Uttar Pradesh, where 785 people died, and deaths were also reported in Nepal and Bangladesh.

"These are some of the worst floods in generations and they present a huge challenge for governments and humanitarian organisations," said Daniel Toole, UNICEF's regional director for South Asia on Friday.

EXTENSIVE DAMAGE

UNICEF said more than 1,000 villages in 13 districts had been affected by the surging waters, which have caused extensive damage to roads and water and electricity supplies.

Prime Minister Manmohan Singh and Sonia Gandhi, head of the ruling Congress party, flew over devastated areas by helicopter on Thursday and announced $228 million in aid.

The London-based humanitarian organisation Oxfam said it was providing those affected with temporary shelter, water purification tablets, buckets and oral rehydration sachets.

The rapid changes in the river's course have forced many harried villagers to move shelters many times and to sell their precious livestock to buy food.

"I sold my goat for just 50 rupees which on any other day could have brought me 2,000 rupees," said Sabia Devi.

UNICEF believes it will be months before the displaced families can return to their homes and expressed concerned over the hygiene conditions of the government-run relief camps.

Cases of diarrhoea were reported from many relief camps in the state.