Detectives investigating the case of a missing four-year-old girl from a Portuguese vacation apartment have reportedly told her parents to stay in the country amid hopes of a breakthrough, a police source told British media Wednesday.

Kate and Gerry McCann of England have been in Portugal since their daughter, Madeleine, disappeared on May 3 from the rented flat where she and her two-year-old twin siblings were sleeping unattended. Her parents were dining at the resort's restaurant 50 metres away.

A family photo shows Madeleine McCann during her family's holiday at Praia Da Luz, Portugal.
(Associated Press)

British media have widely reported that the McCanns were advised against leaving Praia da Luz, as important developments are expected. The two had told newspapers they were making plans to return home.

Also, a senior Portuguese police officer, Chief Inspector Olegario Sousa, said detectives investigating the case have a "positive feeling" about the inquiry as they await DNA results.

Highly trained sniffer dogs were brought from Britain to the resort in the southern Algarve coast after blood was found in the bedroom of the seaside resort. Shortly after, reports came out that the blood was likely that of a Portuguese man who stayed in the room after the McCanns.

A spokesman for the forensic service carrying out the tests said experts were "continuing to examine" samples from the apartment, the Guardian Unlimited reported.

The McCanns have repeatedly said they believe their daughter is still alive.