Newshub Europe correspondent Lisette Reymer says it's been a 'hive of activity' where Portuguese police are searching for Madeleine McCann

Newshub Europe correspondent Lisette Reymer says it's been a "hive of activity" at a remote dam in Portugal after police resumed the search for missing British girl Madeleine McCann.

Portuguese police are searching the Arade dam in the southern region of the Algarve - about 50km inland from a beach resort where McCann disappeared in 2007. This is the first formal development in the case in Portugal in several years.

The investigation is being led by German police who are looking for evidence to tie McCann's disappearance to Christian Brueckner.

The 45-year-old German was made a formal suspect, or an "arguido", by Portuguese prosecutors in 2022.

A source familiar with the investigation told Reuters the operation was likely linked to photographs of the reservoir found at the hideout of Brueckner.

Reymer told AM from the Arade dam in Portugal it's been a "hive of activity". 

"It's been surprising, personally, the scale of it. There have been so many comings and goings throughout the day," she told AM on Wednesday. 

"Police all over this area just combing it with rakes, with spades, with shovels. They've had a lot of heavy machinery here, the forensic teams have been very busy, police officers coming and going throughout the day. There have also been scuba divers that we've seen in action."

The search has been focused on just a small area of land at the moment, Reymer said, with sniffer dogs working throughout the day. 

Around 30 uniformed and plain-clothed officers spent the day searching the scrubland, using pickaxes and inspecting small rocks with rakes and spades. 

The BBC reported police have taken "a number of bags" away from the dam. 

German prosecutor Christian Wolter confirmed they're investigating in Portugal following a "tip-off".

"I can't disclose the background at the moment, like why we are searching there and what we hope to find there. That shall remain our secret for the moment," Wolter said.

In a statement to  German TV channel RTL, Wolter said the tips did not come from Brueckner "but you can imagine that we don't start searching somewhere in Portugal on the off chance, but that there must be a good reason for it". 

Reymer told AM that Wolter urged the public not to get their hopes up as the search continues into its 16th year. 

"He has urged everybody to be patient, to give the team time to do this job and if they have anything to say publicly, they will do so as soon as possible," she said. 

"So just another reminder to the public not to get their hopes up, but to give everyone here a fair chance of surveying this area again properly, because they did do it originally independently in 2008. 

"They want a fair chance to look at this area again and be sure that they have checked it for all the answers possible."

McCann went missing back in 2007, when she was just three years old, from the Praia da Luz apartment she and her family were holidaying in.

McCann's parents, Kate and Gerry, had gone to a restaurant 100 metres away for dinner, while the three kids remained at the apartment. When Kate got back at about 10pm, Madeleine was missing from her cot.

The parents promptly called local Police as a mass search of the apartment complex kicked off, but she was never found.