New Zealand police are open to helping international authorities investigating the disappearance of Madeleine McCann but have received no requests for assistance.

Spokesman Grant Ogilvie said police were aware of developments in the case of the missing British girl through foreign media, who have reported a possible link in the case to Australia or New Zealand.

Private investigators hired by Kate and Gerry McCann are trying to find a "glamorous" Australian or New Zealand woman who spoke to a man in Barcelona just three days after Madeleine vanished in 2007.

The British holidaymaker said she asked him: "Are you here to deliver my new daughter?"

Described as speaking fluent Spanish and in her 30s, the woman is not a suspect, but private investigator Dave Edgar says what she told the man could be significant.

Four-year-old Madeleine disappeared from her family's rented holiday apartment in the Portuguese resort of Praia da Luz on May 3, 2007, while her parents dined with friends at a nearby restaurant.

Mr Ogilvie said New Zealand police were open to help but had not been approached by Interpol.

McCann family spokesman Clarence Mitchell earlier admitted new information linking a New Zealand or Australian woman to the case was vague.

But he suggested there was more to private detectives' search in this part of the world than had been publicly announced.

"We are not doing this in a complete vacuum," Mr Mitchell said. "Anything that is done publicly is part of a wider picture.

"There is other work going on in other directions, some of it perhaps in Australia, some of it perhaps in Portugal, other places too."

Anyone with information Madeleine's on disappearance can visit www.findmadeleine.com.

- With AAP