The mother of missing Madeleine McCann has backed a revamped alert system triggered when missing children are kidnapped or their lives are at risk.

Kate McCann urged members of the public to sign up for Child Rescue Alerts, which will be overhauled later this month.

She said: "When a child is abducted, families are devastated and entire communities are torn apart. The agony of not knowing where your child is is almost impossible to imagine. The helplessness is at times overwhelming.

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"But there is now something we can all do to help. Please sign up to receive alerts - you could save a child's life."

The mother also spoke of how she would prefer to know the truth about what happened to her daughter, even if it is "the worst case scenario".

She said: "If it was down to not knowing or finding out news that isn't what you want to hear? At the end of the day I can't change that. What would you rather?

"I'm not underestimating the blow of hearing bad news that you child had been killed, because obviously we're not going to go 'OK at least we know'. But I've spent hours thinking about that and, each time, I still come up thinking we need to know. Regardless we need to know."

She added: "But there is always the worst case scenario. That's always been a possibility and anyone who thinks that we're blinkered doesn't know us."

The new system will allow alerts to be issued via text, email, social media, digital billboards and to the media.

Members of the public can already sign up to receive alerts, although the new system will come into play on International Missing Children's Day on May 25.

A Child Rescue Alert was recently used in the hunt for murdered five-year-old April Jones, and the system is designed to make the most of the "golden hours" when a child goes missing.

Charlie Hedges from the National Crime Agency, who helped co-ordinate the appeals, said: "The success of Child Rescue Alert is down to each and every one of us. I've already been encouraged by the wide range of organisations who have joined us in partnership to offer their support and help launch this invaluable tool.

"Now it's down to the public to sign up for the alerts so we can send the message as widely as possible when a child goes missing."

Jo Youle, chief executive of the charity Missing People, said "Every minute after their disappearance is crucial to bringing a child home safely. Child Rescue Alert will now mean the public and companies can help - and hopefully save these children's lives."