More than 1,000 birds have been found dead along the shore of India's biggest inland saltwater lake, a senior forest official has told the BBC.
The birds were discovered around Sambhar Lake, 80km (49 miles) south-west of the city of Jaipur, in the northern state of Rajasthan.
The dead include a number of different species, including migratory birds who flock to the lake every year.
The deaths are being investigated by government agencies.
"We are still counting the dead birds," senior forest official Sanjay Kaushik said. "They are strewn over the entire area around the lake. Some 20 to 25 birds who were still alive are being treated."
The first reports of the birds emerged on Sunday, when they were spotted by tourists visiting the lake.
"We have never seen anything like this," Abhinav Vaishnav, a local bird-watcher, told the Press Trust of India news agency.
Vikas Choudhary, a photographer with the Down To Earth magazine who is in the area, said the dead birds were strewn all over an area stretching from 12 to 15km around the lake.
"I am sure the numbers will rise further, and may even touch 5,000 birds. There are just so many dead birds lying all over the place," Mr Choudhary told the BBC.
The birds, which include ruddy shelduck, ruddy turnstone, northern shoveler, blackwinged stilt and common coot, are being buried in deep pits dug near the water.
Forest official Rajendra Jakhar told Press Trust of India that a hailstorm which hit the area a few days ago may have caused the deaths.
"We are also looking at other possibilities, like toxicity of the water and bacterial or viral infection," he said. A local veterinarian has ruled out bird flu as a reason.
Some of the dead birds have been sent to a laboratory in Bhopal for further examination.