Hundreds of people in Peru have needed treatment after an object from space - said to be a meteorite - plummeted to Earth in a remote area, officials say.
They say the object left a deep crater after crashing down over the weekend near the town of Carancas in the Andes.
People who visited the scene have been complaining of headaches, vomiting and nausea after inhaling gases.
But some experts have questioned whether it was a meteorite or some other object that landed in Carancas.
"Increasingly we think that people witnessed a fireball, which are not uncommon, went off to investigate and found a lake of sedimentary deposit, which may be full of smelly, methane rich organic matter," said Dr Caroline Smith, a meteorite expert at the London-based Natural History Museum.
"This has been mistaken for a crater."
A team of scientists is on its way to the site to collect samples and verify whether it was indeed a meteorite.
Geologists have called on the authorities to stop people going near the crash site.
A local journalist, Martine Hanlon, told the BBC experts did not believe the meteor would make anybody sick, but they did think a chemical reaction caused by its contact with the ground could release toxins such as sulphur and arsenic.
An engineer from the Peruvian Nuclear Energy Institute told AFP news agency that no radiation had been detected from the crater. He ruled out any possibility that the fallen object might be a satellite.
Nestor Quispe, the mayor of the municipality to which Carancas belongs, told the BBC that many residents had been affected.
"Lots of people from the town of Carancas have fallen ill. They have headaches, eye problems, irritated skin, nausea and vomiting," he said.
"I think there's also a certain psychological fear in the community."
Local resident Heber Mamani said a bull and some other animals had become ill.
"That is why we are asking for an analysis, because we are worried for our people. They are afraid," he said.
Another local villager, Romulo Quispe, said people were worried that the water was no longer safe to drink.
"This is the water we use for the animals, and for us, for everyone, and it looks like it is contaminated," he said.
"We don't know what is going on at the moment, that is what we are worried about."
The incident took place on Saturday night, when people near Carancas in the remote Puno region, some 1,300km (800 miles) south of the Peruvian capital, Lima, reported seeing a fireball in the sky coming towards them.
The object then hit the ground, leaving a 30m (98ft) wide and 6m (20ft) deep crater.
The crater spewed what officials described as fetid, noxious gases.
Jorge Lopez, a health director in Puno, told Reuters news agency he had an irritated throat and itchy nose after visiting the site.