Massive waves have crashed into the Indian states of Tamil Nadu and Andhra Pradesh, along the country's southern coast, after an earthquake.

More than 2,000 people have been killed, 1,567 alone in Tamil Nadu, its chief minister said.

A nuclear reactor in the state has been shut down after sea water entered an estate housing scientists.

Prime Minister Manmohan Singh made a televised broadcast, saying he was deeply shocked by the devastation.

"My heartfelt sympathies are with the families of the bereaved, and with all those affected in our country," he said.

Many of the victims were simply caught unaware as enormous sheets of water swept them off their feet.

Early morning joggers along the Marina beach in the Tamil Nadu capital, Madras, say huge columns of water surged towards the land without warning.

Bodies of fishermen are said to be strewn on beaches along the 2,000km southern Indian coastline.

Many people were swept several kilometres as powerful waves smashed into their wooden boats.

A resident of Kakinada in India's southern Andhra Pradesh province, P Ramanamurthy, said he saw fishermen being swept out to sea.

"I was shocked to see innumerable fishing boats flying on the shoulder of the waves, going back and forth into the sea, as if made of paper," he told the Associated Press news agency.

"Many boats were upturned, but fishermen were still holding onto them," he said.

Stranded

The BBC's Sampath Kumar in Madras says water came several kilometres inland.

Sea water flooded the streets of Cuddalore, some 150km south of Madras, overturning several cars and leaving nearly 800 people dead.

Indian air force helicopters have been pressed into service to evacuate people living in the submerged areas.

Nearly 500 tourists have been stranded on the Vivekananda rock memorial, a popular tourist destination on an Indian Ocean island, a few kilometres off the tip of the mainland.

Andamans hit

More than 100 people are also feared dead on India's Andaman and Nicobar Islands, which lie close to Indonesia.

The BBC's Geeta Pandey, who is in the capital Port Blair, says jetties on the island's main port have collapsed and many people have been forced out of their homes, which are flooded.

The main road on the highway is badly damaged with enormous gashes on its surface.

An islander, Kakoli Roy, wept as she surveyed her damaged home with most of her furniture and household belongings ruined beyond repair.

"This is our whole life's acquisitions gone in a second," she told the BBC.

"My husband retires from his job next year and we have no other source of income. I don't know what we'll do."

Military deployment

In Andhra Pradesh state, tidal waves flooded the Vishakapatnam port, one of the country's major commercial and naval harbours.

A lighthouse collapsed and several houses and buildings have developed cracks, forcing residents to be evacuated.

The authorities there say army, navy and air force personnel have been called in to help with the rescue and relief operation.

Twelve people have also died in Kerala, on India's west coast and a key tourist destination.