Nurses in some Belfast hospitals have been left stretched outside normal office hours, senior medics have claimed.
Clinicians told inspectors reviewing services at nights and weekends that staff levels to manage patients were under pressure, a report said.
A report by the Regulation and Quality Improvement Authority (RQIA) stated: "In the Belfast Trust nurse staffing levels were considered to be stretched to manage the complexity of patients in hospitals; clerical support is limited at weekends which can delay processes; there can be delays in discharging patients at weekends and transferring patients at night.
"At Ulster Hospital nurse staffing was also considered to be stretched and arranging discharges and transfers could be difficult at nights and weekends."
Many hospital patients did not get enough sleep at night because of noise, it was revealed. Temperature and brightness on the ward also contributed to the insomnia, inspectors said.
The RQIA reviewed standards of care after concerns were raised about significant patient death rates in the UK.
It said at times pressures to accommodate emergency admissions during the night can lead to the transfer of patients between wards, and there may also be difficulties in providing staff to accompany those who need to be transferred between hospitals.
While 70% of those who responded to a survey of patients felt they did get enough sleep on the ward, only 30% from the Patient Client Council felt the same.
The RQIA's chief executive, Glenn Houston, said: "During the review, RQIA found that there were differences between acute hospitals in the availability of services and staffing at nights and weekends."