Detectives are investigating more than 100 Madeleine McCann ' sightings' in Belgium following a warning she could have been stolen to order for a paedophile ring.

Interpol officials in Brussels said they had received 107 reports since she vanished from Portugal on May 3 last year.

It is understood to be the largest number of reported sightings outside Spain and Portugal.

Leads: Detectives are looking at 100 possible sightings of Madeleine in Belgium

Private detectives working for Kate and Gerry McCann have said that they will check the most credible sightings.

It emerged yesterday that a secret British police report had warned of 'intelligence' suggesting Madeleine had been sold to a Belgian child sex gang by a 'spotter' in the Algarve.

Scotland Yard attempted to play down the email, sent by one of its officers in March this year, and said the tip-off was unproven and could have been wrong.

But the mammoth Portuguese police files released this week revealed a series of sightings around Belgium in May and June last year. 

On May 15, Belgian woman Line Compere reported seeing a girl resembling Madeleine with an Eastern European couple on a tram in Brussels.

She said: 'It was obvious she was not their child and they were behaving quite strangely. I thought she looked lost somehow.

At that point I had not seen a picture of Madeleine and I didn't know what she looked like, but when I saw a picture of her later I knew it was her.'

Twelve days later a British man said he saw a similar-looking girl asleep on a train from Brussels to Antwerp and feared the child could have been drugged.

Then on June 2, Belgian man Gilles Crippiau told police about a sighting in a shop in the town of Mouscron near the French border.

The girl, who had big eyes and a pale, 'tired' face, was with an English-speaking woman who drove her away in a grey Renault Scenic.

Missing: Line Compere saw the group on a tram heading to the Midi Station, above

Mr Crippiau said: 'Once back home I looked at a photo of the little McCann child and I was struck by the resemblance to the girl I had seen in the shop. '

Belgian police contacted the shop's manager but were told there were no CCTV cameras inside. Meanwhile a Dutch witness who said she saw a girl in Amsterdam who called herself 'Maddie' has met with the McCann's spokesman Clarence Mitchell.

Anna Stam, 41, was flown to Britain by a tabloid newspaper and is understood to have helped draw an artist's impression of the people she saw.

Interpol official Alain Remue, the chief commanding officer of the Belgium Federal Police's missing persons unit, said a special hotline had received 107 witness reports related to Madeleine's disappearance.

He said 67 were too vague to be properly investigated. The remaining 36 were investigated and passed to Interpol's Lisbon bureau but there was no response from Portugal. Portugal's attorney-general formally shelved the investigation last month and cleared Mr and Mrs McCann, both 40, as official suspects in their daughter's disappearance.

Mr Remue said his officers had been able to rule out some of the Belgian sightings, including a 'strong' witness report from the Dutch border last August. The girl was later found to be a Dutch girl who was seen with her family.

The Portuguese police files detail only a handful of the Belgian sightings.

The Worldwide Hunt

Sightings of Madeleine McCann across the world have varied from the credible to the absurd.

One well-meaning British diplomat even sparked a major incident in Guatemala when he thought he had seen the girl.

The Consul to the Central American republic told police he believed he had seen a girl who 'bore a striking resemblance to Madeleine' in a shopping mall in Guatemala City in June last year.

It proved to be a false alarm but the girl's father, one of the city's leading lawyers, accused the British Government of intending to kidnap his daughter and demanded a formal written apology from the British Embassy.

There have also been incidents where would-be helpers have accosted parents with blonde daughters, demanding to see their eyes to check if they have Madeleine's distinctive fleck. The McCann's spokesman Clarence Mitchell said: 'Investigators have the capacity to move quickly to any part of the world.

'For example there was a sighting in Chile a couple of months ago and we had people on the ground - within the building she was supposed to have been seen in - in three hours.'