LONDON (AFP) - A new British police television appeal about the 2007 disappearance of British girl Madeleine McCann in Portugal has triggered an unprecedented public response, programme makers said on Tuesday.

British detectives who have spent two years raking over the case published new electronic images of men they want to trace, plus a reworked timeline of events leading up to Madeleine's disappearance.

Police said the appeal, broadcast on Monday on BBC TV's Crimewatch, triggered more than 300 calls and 170 emails from the public.

They are keen to find one man seen carrying a young child in the Algarve resort of Praia da Luz on the night of May 3, 2007, around the time Mrs Kate McCann discovered her eldest daughter was missing from their holiday apartment.

London's Metropolitan Police said the man was of "vital importance" in their quest to discover what happened to Madeleine, who vanished just a few days before her fourth birthday.

Crimewatch editor Joe Mather told BBC radio: "It's been a truly unprecedented response.

"There were lots of calls from British people who were in Praia da Luz around the time of Madeleine's disappearance who'd never previously spoken to the Met.

"Several callers mentioned the same name" for the man seen carrying a child, he said.

"It is a long shot but it's remarkable how often results are possible even several years down the line.

"The ability to rule people out of an investigation or out of a timeline can be almost as significant as being able to name potential suspects.

"There were genuinely useful calls."

Detective Chief Inspector Andy Redwood, the senior investigating officer in the case, said his team had had a "revelation moment" that put the spotlight on other possibilities.

Their probe focused on the time between 8.30pm, when the McCanns left their three children in their apartment to dine with friends at a nearby tapas restaurant, to when Mrs Kate McCann discovered Madeleine was missing at 10pm.

They established that a man seen carrying a child near their apartment at 9.15pm by a friend of the McCanns, was almost certainly an innocent British holidaymaker collecting his own daughter from a nearby creche.

That put the spotlight on other events leading up to 10pm.

The new e-fits of the man whom police are especially keen to trace were drawn up based on descriptions from different witnesses. They said the blonde-haired child did not seem in distress.

The witnesses described the man as white, between 20 and 40 years old, with short brown hair, of medium build and height and clean-shaven. One image shows him with a fuller jaw than the other.

Police said they were working on the theory that the abduction could have been planned and were also interested in tracing "one or two" fair-haired men who had been seen "lurking" around the apartment complex before Madeleine's disappearance. Witnesses said the men were speaking German or Dutch.

They also speculated that the youngster may have disturbed a burglary, pointing to a sharp increase in local break-ins in the months leading up to the incident.

The appeal will also be broadcast in Ireland, Germany and The Netherlands - though there are no plans to show it in Portugal.

Detective Redwood was to visit The Netherlands on Tuesday and Germany on Wednesday.

German public broadcaster ZDF's Aktenzeichen XY programme will on Wednesday show the images of the key man police want to trace.

The force announced it was offering a new reward of up to £20,000 (S$39,800) for information leading to the prosecution of McCann's abductor.

Portuguese authorities closed their investigation in 2008, but the Met Police spent two years reviewing the case at the British government's request and opened their own probe in July this year.

The operation has interviewed more than 440 people and identified 41 "persons of interest".

During Crimewatch, the McCanns, who launched a global media campaign to find their daughter, said they were still optimistic she could be traced.

"We're feeling hopeful," said father Gerry McCann. "These cases can get solved", he said, citing instances where long-lost people have been found.