About a quarter of medical staff there are reportedly off sick with Covid-19.
Now 10 hospitals have requested that staff who have tested positive but do not have symptoms keep working.
The head of the Belgian Association of Medical Unions told the BBC they had no choice if they were to prevent the hospital system collapsing within days.
Dr Philippe Devos acknowledged that there was an obvious risk of transferring the virus to patients.
One in three people tested are coming back positive with the virus in the eastern Belgian city. Hospitals are transferring patients elsewhere and cancelling non-urgent surgeries, days after Health Minister Frank Vandenbroucke warned the country was close to a "tsunami" of infections where authorities "no longer control what is happening".