Two babies have died at the Royal Hospital in Belfast after an outbreak of an infection, Belfast Health Trust said.
Pseudomonas can be particularly harmful to infants who are already ill, a spokesman for the organisation added.
Admission to the neonatal unit is being restricted.
The hospital representative said: “Sadly two ill babies have died whose deaths may be linked to this outbreak. We are supporting these families at this very difficult time.
We are in the process of investigating the outbreak and taking all steps to identify the source.”
To help prevent the spread of this infection, everyone, including parents and guardians, are being asked to be diligent in their hand hygiene when entering and leaving the unit.
The situation will be kept under constant review.
Sinn Féin MLA Michelle Gildernew said: “This outbreak is extremely concerning. It has obviously seen the tightening of access to the maternity ward and I will be seeking reassurances that all is being done to protect those in the ward, especially any infirm babies who are more susceptible to this virus."
“We must now, as a matter of urgency, investigate how this particular outbreak occurred, isolate the cause, and ensure that all measures are taken to stop any further spread of this disease or any further re-occurrence."
PA