One person has died and more than 400 have been hospitalised in southern India due to an unidentified infection that caused many to fall unconscious following seizures and nausea, a senior health department official said.

Government and medical authorities in the southern state of Andhra Pradesh said that more than 200 people were discharged at the weekend.

They said that tests had ruled out Covid-19, the infection caused by the novel coronavirus. Further serological tests are under way.

"The causes of the outbreak are not known yet," the state government said in a statement, adding that people in all age groups appeared prone to the infection.

Separately, India's federal health ministry said it would send a team of three medical experts to investigate the outbreak, which has infected more than 300 children, it said.

"The children reportedly suffered from dizziness, fainting spells, headache and vomiting," the ministry said, adding that a door-to-door survey was also under way.

The state health department were alerted to the first case over the weekend following the death of a 45-year old man, said Geeta Prasadini, a public health director in Andhra Pradesh state.

"We have taken the patients' blood samples for serological investigation and bacterial investigation to rule out any type of meningitis," Ms Prasadini said.

Authorities were investigating water supplies at 20 locations within the city of Eluru where the outbreak was first reported, as well as neighbouring areas, she added.

The state of Andhra Pradesh is also among the worst-affected by Covid-19 in the country.

India, which has recorded 9.68 million Covid-19 infections, is just behind the United States in the global tally.