Police investigating Madeleine McCann's disappearance have sealed off a search area as they prepare to begin excavations in Praia da Luz.

A team of Portuguese police officers and at least four vehicles have been stationed on a mound to the west of the town since early this morning.

They are expected to be in the area for days, rather than hours, as they work to identify anomalies in the terrain which may merit further investigation by digging.

The development marks a significant new phase of the investigation into Madeleine's disappearance while she was on holiday with her family in the Portuguese resort in May 2007.

Several parts of the town have been identified as potential search sites including an area of scrubland close to the apartment where the McCanns had been staying.

The land which had been earmarked for development is now fenced off but was an open area on the night Madeleine vanished.

Her parents Kate and Gerry McCann have not travelled to Portugal but will be kept up to date with any developments.

Former Metropolitan Police search adviser Keith Farquharson said: "They wouldn't just be identifying that part by plucking it out of thin air they have obviously got hard information and the evidence trail is leading to that particular area." 

Mr Farquharson explained what is likely to happen next: "The area will be properly mapped with GPS coordinates for each one of those sites.

"Those areas will then be broken into smaller areas which will be easier to search, then you would send in the ground penetrating radar which will look for anomalies below the surface.

"Once those anomalies are identified then in my experience you would deploy victim recovery dogs to those particular areas."

As they are working alongside the Portuguese authorities the Metropolitan Police are giving out very few details about the new phase of the investigation or how long it will last.