A new children's hospital which failed safety checks days before it was due to open is to remain closed while water, ventilation and drainage systems are assessed.

Health Secretary Jeane Freeman, who overruled NHS Lothian over plans to open the Royal Hospital for Children and Young People (RHCYP) in Edinburgh at the start of July, admitted it is not known when the site will be safe for use.

Patients, staff and services at NHS Lothian's Royal Hospital for Sick Children were expected to transfer to the RHCYP on July 9, but the plans were halted after final checks revealed the critical care department's ventilation system did not meet national standards.

Ms Freeman postponed the move and now says that NHS National Services Scotland (NSS) are working at the site to "give quality assurance on the water, ventilation and drainage systems and establish a timeframe for services to move safely to the new hospital."

Other newly-built hospitals and NHS buildings will also be reviewed by NSS to check whether they meet the required standards.

Ms Freeman said: "I understand that this is a disappointing and worrying time for parents and carers of patients who have appointments at the new children's hospital.

"However, safe, effective and high-quality clinical services continue to be delivered from the existing site in Sciennes.

"Infection prevention must always be embedded within the design, planning, construction and commissioning activities of all new and refurbished healthcare facilities, which is why I have also instructed NSS to review current and recently completed major NHS capital projects and provide assurances that the same standards have been adhered to."

READ MORE: Staff bid farewell as Edinburgh's Sick Kids' hospital prepares to close

Thanking staff, she added: "I recognise and appreciate that NHS Lothian staff have made considerable efforts both in the lead up to the planned move and following the delay.

"I have written to staff today to thank them for their hard work and for all that they are doing to help manage the situation, and for their excellent track record of providing high-quality patient care."

An investigation into causes of the delay has already been launched and is being carried out by KMPG, Ms Freeman announced.

However, the Scottish Conservatives have demanded a full investigation into the issues at the new hospital, which they say has "been plagued by problems from the start".

READ MORE: Opening of new hospital cancelled over ventilation problems

The party's health spokesman Miles Briggs said: "All of these measures announced by the SNP Government will only delay things further.

"This is a much-needed facility which was supposed to open in 2012 - the SNP has been in charge the whole time and must take final responsibility for the failure of this project.

"Families and staff will look at this announcement and wonder why these things weren't demanded of the construction firms from the outset.

"After all, the nationalists have had seven years of delays in which they could have ensured these boxes were ticked.

"The only way to establish the extent of what has gone wrong, why it has happened, and how we can ensure it's not repeated, is to have a full Scottish Parliament inquiry.

"It's the very least patients, their loved ones and the hardworking staff deserve."

READ MORE: Legal threat against builder over delayed sick kids' hospital 

Calling for the Health Secretary to "get a grip on this latest NHS scandal", Scottish Labour health spokeswoman Monica Lennon said: "Patient and staff safety comes first but the lack of clarity over when the new Edinburgh Sick Kids hospital will be opened is completely unacceptable.

"Patients and staff who were due to move into the new building this month have been left in limbo, and Jeane Freeman hasn't even indicated if the new hospital will be safe for use this year.

"Serious safety concerns about the condition of the building should have been raised well in advance of its opening, so it's beyond belief that patients and staff find themselves in this situation."

The Scottish Government explained that parents and carers are being contacted directly by the existing Royal Hospital for Sick Children to confirm arrangements for their child's appointment.

Those with appointments in July are being contacted by phone and those with appointments in August onwards will be contacted by letter.

Speaking after the delay was announced Jacquie Campbell, chief officer of acute services at NHS Lothian, said: "I would like to apologise to patients who may be confused and worried about the plans for their care and reassure them that we have a raft of contingency plans in place.

"The most critical point is that A&E will not move. In an emergency, patients

should still take their children to the building in Sciennes."

A dedicated helpline number has been set up for families and carers, and anyone with concerns about appointments or treatment can call it on 0800 028 2816.