The police investigation into missing Madeleine McCann has been defended by the Portuguese ambassador in London.
Madeline disappeared while her parents were at a nearby restaurant
Antonio Santana Carlos said the case was of "great concern" to Portugal and asked people to trust the police.
Little information has been made public, prompting concerns the police are not doing enough.
Three-year-old Madeleine, who is from Leicestershire, disappeared from a holiday resort in the Algarve village of Praia da Luz on Thursday.
The police are expected to give an update on their investigation at about 1830 BST on Tuesday.
There have been reports on Portuguese state television that a man and a child matching Madeleine's description were seen driving off in a car from the town of Nelas, about 300 miles (483km) north of Praia da Luz.
The channel reported that police road blocks had been set up in the area.
Meanwhile, Manchester United footballer Cristiano Ronaldo, who is Portuguese, said he was moved by news of the little girl's disappearance.
He made an appeal for information about her whereabouts on MUTV, Manchester United's television channel.
"I appeal for anyone with information to come forward," he said.
Earlier, Madeleine's parents Gerry and Kate made a private visit to the local church of Nossa Senhora Da Luz (Our Lady of Light) to pray for her safe return.
Clutching Madeleine's favourite soft toy and a picture of her, Mrs McCann walked with her head bowed.
The couple were accompanied by a member of staff from the Mark Warner resort where Madeleine went missing.
The McCanns have said their Catholic faith has offered them hope and strength.
In an a interview with the BBC, Mr Carlos said that under Portuguese law there was very little information the police could disclose.
He said: "We are cooperating with Europol and Interpol and also with the British police.
"So for the police of course it is a completely open matter, but investigation is quite secretive and it has to carry on that way, due to our legal obligations that exist in Portugal."
He added: "I ask you to trust the authorities. They are doing their best. If they cannot give you more information, it's because they can't."
Police said they had widened their search to nine miles (15km) from Praia da Luz and are working with UK and other forces, taking witness statements and making inquiries into whether paedophile rings operate in the area.
Dave Shelton from Manchester, who now lives in the village, has been working with the police to co-ordinate volunteer searchers.
He told BBC News that a group of up to 20 locals and tourists were searching an area around the village, concentrating on ruins, wells and bushes.
Kate McCann clutching Madeleine's favourite soft toy
He said: "Every morning at eight I go to see the police chief and he decides where we go and gives us our little zone, plus a map.
"We go off and do that area and then report back and tell him we have done the area so he can tick it off."
As the search continued, back in the Leicestershire village of Rothley, friends and neighbours of the McCanns are to hold a silent vigil for the family and people are being encouraged to light a candle or to tie a ribbon around railings at the war memorial.
Staff at Leicester's three hospitals also joined in prayer for the McCann family.
Madeleine's father is a consultant cardiologist at the city's Glenfield Hospital and her mother is a GP.
Madeleine's family have confirmed she was wearing white pyjama bottoms with a small floral design and a short-sleeved pink top with a picture of Winnie the Pooh character Eeyore when she disappeared.
A set of pyjamas identical to the ones Madeleine was wearing
She is believed to have been taken from her bed while her parents were eating at a nearby restaurant and regularly checking on her and their two-year-old twins Sean and Amelie.
Around the marina in the nearby town of Lagos, maritime police have been searching amid claims a man was seen with a small girl in the area.
And tourist Amanda Mills, 34, from Basildon, Essex said that two weeks ago she saw a man trying to steal a pushchair at the resort when Madeleine went missing.
Mrs McCann found the outside shutter and window to Madeleine's room had been opened and her daughter missing shortly before 2200 local time on Thursday.
The complex where Madeleine disappeared