Police in Portugal are investigating an anonymous letter and a map claiming to show where missing four-year-old Madeleine McCann's body is buried.
Madeleine McCann has now been missing for more than a month
The letter, sent to Dutch paper De Telegraaf, identifies an area 15km (9.3 miles) from where Madeleine vanished.
It strongly resembles another letter sent to the same newspaper last year, accurately pinpointing where two missing Belgian girls were buried.
Ch Insp Olegario de Sousa said officers were "checking the information".
Around eight plain-clothed police officers visited the village of Arao, which is 15km from Praia da Luz, on Wednesday evening.
It is understood that a formal request was made to a section of the police called the GNR to carry out searches in the area.
They spent an hour and 20 minutes looking at fields and the surrounding area ahead of possible searches on Thursday morning.
The Madeleine letter pinpoints a dirt track north of Odiaxere in the Algarve, according to De Telegraaf.
The paper said that the letter claims Madeleine, of Rothley, Leicestershire, is buried "north of the road under branches and rocks, around six to seven metres off the road".
Beside a cross and two question marks, the sender has written "vermoedelijke vindplaats Madeleine" - the place where Madeleine can probably be found.
Portuguese police would not confirm whether they had begun searching the area.
But Mr Sousa confirmed Portuguese police were aware of the map and were doing "everything necessary".
He said: "There have been exchanges between Dutch police and us.
"The information indicated an area 15km from the place of the disappearance of the little child. It is not far from Praia da Luz. We are checking the information like we check everything in this case for importance."
Asked if a search would include digging, he replied: "If the information gives us a precise location where we can look, we will do it."
The BBC's Caroline Hawley said it was difficult to assess the reliability of the map, given that Portuguese detectives had received hundreds of tip-offs which have not proved useful in the course of the investigation.
Officers also reported that the map was vague, she added.
Dutch police are studying similarities between the new letter and one received by De Telegraaf pointing to the whereabouts of Belgian step-sisters Stacey Lemmens, seven, and Nathalie Mahy, 10.
The girls were murdered in June 2006 after they disappeared from a late-night fair in the town of Liege.
On the day that the letter was received, police found their bodies at the spot indicated on an enclosed map.
A convicted paedophile, Abdullah Ait Oud, is now on remand awaiting trial for murder.
The Telegraaf believes the letter comes from the same sender because the phrase "vermoedelijke vindplaats" was also used in the tip-off letter last year about Stacey and Nathalie, BBC correspondent Alix Kroeger added.
Madeleine disappeared while on holiday with her parents in Praia da Luz on 3 May.
It is believed she was abducted from a holiday apartment while her parents ate at a nearby restaurant.
Her parents, Kate and Gerry McCann, have travelled across Europe in an effort to find her.
The couple were also featured in an appeal for information on BBC One's Crimewatch.