The construction of the new National Children's Hospital is falling behind schedule.
The Health Service Executive (HSE) has warned that the project is facing delays which could affect critical timelines.
Work on some parts of the National Children's Hospital at the St James's site in Dublin are behind schedule.
HSE chief executive Paul Reid has written to board members, to warn them that the delays could lead to important deadlines being missed.
In a statement, the National Paediatric Hospital Development Board said: "Throughout the lifetime of the project, different aspects may be ahead or behind projected timelines and such issues are constantly being reviewed and worked through.
"The main construction contractor is currently reporting to be behind on certain elements of the construction, however, a revised programme timeline is currently being developed which will set out mitigation measures.
"Under the construction contract the new children's hospital is scheduled to be completed in Q3 2022 and it will open in 2023, after a period of commissioning."
The board added that the structural frame on the construction site is now reaching roof level in most advanced areas of the building.
This means the building is now being visible well above the hoarding.
Basement excavation, with the exception of the temporary road, is also complete as is piling.
The mechanical and electrical fit out of the basement and plant areas has begun and the façade works on the south fingers adjoining the South Circular Road will commence this month.
The hospital is currently due to open in April 2023.
The estimated cost of the project has risen by €450m to €1.7bn since it was first announced by the Government.