The search for a toddler missing for three days in a tiny hamlet in the French Alps will continue with more police resources, investigators said on Tuesday.
Local prosecutor Remy Avon said there was "no clue, no information, no element allowing us to understand the disappearance" of Emile, 2.
If he was simply lost then "medically, beyond a period of 48 hours, given the child's young age … and the current intense heat … his life is very much at risk", Mr Avon said.
Emile was staying with his grandparents when he went missing on Saturday.
He was last seen by two neighbours walking alone on a street of Haut-Vernet, a tiny village of 25 inhabitants at an altitude of about 1,200 metres.
Dozens of police and soldiers backed by dogs and a helicopter searched 30 buildings, 12 vehicles and 12 hectares of terrain around Haut-Vernet and even haystacks, and interviewed 25 people, Mr Avon said.
The site was off-limits to outsiders from early Tuesday.
"We're pushing on-the-ground investigations as far as we can," Mr Avon said. "We're at the same point as yesterday and the day before."
He said that while the search would continue on Wednesday, the investigation would enter "a second phase", analysis of search results.
"We will have to give the police time" to work, Mr Avon said.
He said that the number of gendarmes working on inquiries had been increased to 20 and it would be categorised as a nationwide investigation, meaning access to more resources.
Large-scale searches involving volunteers, which took place on Monday, were discontinued.
Mr Avon had earlier said that investigators were also looking at details such as local phone records to determine "what phone calls were made, by whom and to whom", about the time of the disappearance.
They were also checking which mobile phones were connected to local towers.
"All possible explanations are on the table. We're not favouring any, and we're not ruling any out," Mr Avon said.
The terrain in the search zone is hilly and craggy with many streams, and the region has been hit by a heat wave, with a maximum of 35ºC on Tuesday, according to weather authority Meteo France.
The search has focused on an area of 5km around the hamlet.
"The child should have been found after 48 hours in that perimeter," regional prefect Marc Chappuis said on Monday.
Police, still hoping for a breakthrough thanks to witness statements, have circulated a picture of the blond boy with and hazel eyes who was wearing a yellow top, white shorts and hiking shoes the day he disappeared.
About 1,200 people have called a tips line, but Mr Avon asked people not to overwhelm investigators with possibly irrelevant information.
Hundreds of volunteers have taken part in efforts to find the boy.
"We took part in a big search this morning with 50 other people," said Roxane, 19, who went with two friends to help on Monday.
"There was a gap of two metres between each of us. We looked in the fields and in the woods. We looked out for the smallest clue, maybe an item of clothing or a shoe he could have lost."
Prosecutors have given no information about the number of adults in the grandparents' house when Emile disappeared.
