Swiss police said today they have halted their ground search for missing six-year-old twins and will shift the focus of their probe after witnesses confirmed the girls had been last seen in France.

"Everything about concrete searches on the ground has been stopped," said Jean-Christophe Sauterel, a spokesman for police in Vaud canton told AFP.

"All that could be done in our view, has been done today," he added.

Swiss police had deployed helicopters, dogs and teams of inspectors to scour areas close to the village of St Sulpice, in western Switzerland, where the twins lived, after their father failed to return them to his estranged wife on January 30.

But witnesses have come forward since to say that they had seen Alessia and Livia on board a ferry between Marseille and Corsica with their father Matthias Schepp, who later killed himself in southeastern Italy last week.

The spokesman said that police are now working on "understanding what has happened... to find places where the father liked to go to with his daughters."

He added that it was "essential to reconstruct the journey taken by the father in order to find the girls."

The mother of the twins, Irina Lucidi, made an emotional plea on Italian television Wednesday, urging viewers to contact the police if they had any information that could bring an end to her ordeal.

"I appeal to whoever has seen them or knows something to contact the police," an emotional Irina Lucidi said on RAI 3's primetime news bulletin.