The opening of the long-awaited new children's hospital in Edinburgh has been cancelled due to a problem with the ventilation system.

Patients were set to begin moving from the current building near the Meadows into the new The Royal Hospital for Sick Children and Young People in Little France on Friday.

It was due to fully open on Tuesday, the same day as the old hospital was set to close.

However, a problem has been uncovered in the critical care unit of the £150m new building, on the site of the Edinburgh Royal Infirmary.

Health Secretary Jeane Freeman said she was "disappointed" and has ordered an investigation.

The hospital was initially due to open in 2017, but has faced a myriad of problems, including two construction companies going into administration.

Previous issues with ventilation as well as problems with fire detection and drainage have also caused delays.

Health Secretary Jeane Freeman said: "There is no greater responsibility of the NHS than to ensure the clinical safety of their patients, not least when those patients are children.

"In order to be absolutely sure that patient safety is delivered, I have no choice but to postpone NHS Lothian's planned move to the Royal Hospital for Children and Young People.

"It is vital that patient safety remains paramount, which is why I have asked the health board to stop all moves until assurances have been given that the new site is entirely compliant with the relevant health technical standards."

She added: "While this issue has been caught by the final safety checks, I am disappointed and deeply concerned that this was not identified earlier.

"I have asked that Health Facilities Scotland undertake an investigation to determine how the hospital got to this advanced stage before it was discovered that the ventilation system fell below the standards expected."

NHS Lothian chief executive Tim Davison said there was no choice but the delay the new hospital's opening.

He said: "Patient safety is paramount, and following the handover of the new hospital NHS Lothian has continued to monitor facilities at the new site to ensure all systems are operating to national standards.

"Following advice from an independent advisor, I fully accept the Health Secretary's decision to reschedule the move to the Royal Hospital for Children and Young People.

"The air environment is extremely important and can help prevent the occurrence and spread of infection in patients who are already vulnerable.

"We are extremely disappointed that we cannot move as planned and I am very sorry for the disappointment this will cause to patients, their families and staff affected by this delay. However, patient safety must always come first."

Views of children and staff were taken on board when designing the look of the new hospital.

A spinal wall feature, which runs throughout the hospital, shows the texture of skin taken from imprints from three patients and magnified to show up in 3D.

The 242-bed hospital will include ten theatres, four MRI scanners and outdoor play areas.

The main waiting area even features a dragon, as well as a number of interactive games.

Health chiefs hope these features will help patients feel as relaxed as possible when coming to hospital.