Princess Kate and Prince William have condemned the "heinous" Southport stabbings, adding that they "cannot imagine what the families went through".

A 17-year-old boy from Banks in Lancashire remains in police custody following the stabbings - but the incident is not being treated as terror-related.

The royal couple said in a statement: "As parents, we cannot begin to imagine what the families, friends and loved ones of those killed and injured in Southport today are going through.

"We send our love, thoughts and prayers to all those involved in this horrid and heinous attack.

Princess Kate and Prince William 'cannot imagine what the families went through' following Southport stabbingsPA/Getty

"Thank you also to the emergency responders who, despite being met with the most horrific scenes, demonstrated compassion and professionalism when your community needed you most."