A bacterial infection that can cause potentially deadly illnesses has broken out at Harland and Wolff shipyards in Belfast.
The Public Health Agency (PHA) said the pneumococcal disease had been detected in a number of employees.
The bacteria can cause a variety of infections, including pneumonia, meningitis and blood-poisoning.
It is understood four employees have been struck down, with tests being carried out on others.
A spokesman for the PHA said: "The Public Health Agency (PHA) is working with the Health & Safety Executive Northern Ireland (HSENI) and Port Health colleagues to investigate a cluster outbreak of pneumococcal disease at Harland and Wolff, Belfast.
"A small number of employees working at Harland and Wolff have been confirmed as having pneumococcal disease.
"The PHA is working closely with Harland and Wolff and hygiene advice has been given to employees. Vaccination is being offered to employees working in high risk exposure areas as a preventative measure."
The PHA said there was no wider risk to the public.
The PHA said welders or people exposed to welding fumes in their job were among those at more risk of developing a pneumococcal infection.
Throughout Northern Ireland, there are around 50 to 60 cases a year of invasive pneumococcal disease each year.
The bacteria which cause the infections can be spread by close contact with someone who is carrying the bacteria when that person coughs or sneezes.
They can also be spread by direct contact with respiratory secretions from an infected person, such as used paper tissues.
The PHA said people can carry the bacteria in the backs of their noses and throats without ever becoming ill, while others can go on to develop an infection.
Apart from welders, other groups of people more at risk of developing it include: the very young or the very old; those with a chronic illness such as diseases of heart, lung, kidneys, liver or diabetes; those without a spleen or with a damaged spleen; and those whose immune system is not working properly.
It is understood not all the infected employees worked in the same areas of the business, with two based in offices.
A spokesman for Harland and Wolff Heavy Industries Ltd said the company was "co-operating fully" with the PHA.
The Harland and Wolff spokesman added: "None of the work schedules at the yard are affected and all projects continue as normal."