London's Metropolitan Police said they are still investigating the disappearance of the girl, who vanished shortly before her fourth birthday in May 2007.
Detective Chief Inspector Andy Redwood said he is leading a team of more than 30 police officers focusing on the case. He said police also have to consider that she may be dead.
"Our drive on both scenarios is of equal measure," he said.
Police have released a new image of the girl, who would now be nine if she were alive.
Redwood said forensic evidence of the sequence of events around her disappearance shows there are moments when she could have been snatched by criminals but said he had an "open mind" on who could have abducted her.
Her disappearance has drawn global media attention, partly because her parents, Kate and Gerry McCann, were at one point questioned as suspects by the Portuguese police. They were cleared of any part in the disappearance.
Portuguese police closed their investigation in 2008 but Redwood said Scotland Yard says it wants the case reopened. Redwood said his officers are reviewing all the evidence that has been gathered so far by British and Portuguese police and by private investigators hired by McCann's parents.
He said they have identified 195 things that could be investigated further from the material they have reviewed, and said much of it would have to be translated from Portuguese.
There has been no reliable indication of what might have happened to the girl despite numerous reported sightings from around the world.
Redwood said he has made seven visits to Portugal and is working closely with Portuguese police officers. He has had regular contact with the missing girl's parents and U.K. police have also worked with Spanish authorities on the case.
Kate and Gerry McCann have pressed to keep the case in the public eye, publishing a book and appearing on the "Oprah Winfrey Show."
UK police said the investigation has cost 2 million pounds ($3.2 million) so far.
