India is rushing a team of medical experts to southern Andhra Pradesh state after a 'mystery' illness killed one and sent hundreds to hospital.

An MP from the ruling Bharatiya Janata Party said that preliminary blood tests have revealed high amounts of lead and nickel.

Patients showed a wide range of symptoms from nausea to fits and fainting, doctors said.

This comes as India battles a pandemic, with a high coronavirus caseload.

Andhra Pradesh has been one of the worst-affected states - at more than 800,000, it has the country's third-highest case count.

But Covid-19 doesn't appear to be the cause of the hospitalisations over the weekend. The state Health Minister, Alla Kali Krishna Srinivas, said all the patients had tested negative for coronavirus.

Mr Srinivas said the patients' blood samples did not reveal any evidence of a viral infection.

"We ruled out water contamination or air pollution as the cause after officials visited the areas where people fell sick," he said. "It is some mystery illness and only lab analysis will reveal what it is."

However, BJP MP GVL Narasimha Rao sent a text message to local journalists saying that preliminary blood tests, conducted by the All India Institute of Medical Sciences (Aiims) in Delhi, had shows that most of the samples contained lead, nickel and other heavy metals.

A statement released by the Indian health ministry said that Vice President Venkaiah Naidu spoke to the director of Aiims, India's leading public hospital, and was informed that experts in poison control were in touch with doctors in Eluru town, where most of the illnesses occurred.

Officials said so far 500 cases were recorded - 300 of them had been discharged and 19 were moved to other hospitals in the state for better treatment.

Chief Minister Jaganmohan Reddy visited the Eluru Government Hospital and met patients undergoing treatment.

Experts from the World Health Organisation (WHO) are also expected to arrive in Eluru for further investigations, medical officials have told media.

The opposition Telugu Desam Party has demanded an inquiry into the incident, insisting that contamination was the cause of the mystery illness.