A 23-year-old Malaysian man was detained at House of Zen in St Anne's Square last Thursday evening, where he had been working illegally.
On the same night, officers also visited SAFA Indian restaurant in Bank Street and arrested a 25-year-old Nepalese man and three Bangladeshi men aged from 30 to 42.
All five are being held by the Home Office pending their removal from Northern Ireland.
Mike Golden, from the Home Office immigration enforcement team in Belfast, said: "We are determined to stamp out abuse of the immigration system.
"We want the public to contact us if they have any information on businesses or people who are breaking immigration law.
"Employers who take on illegal workers are both fuelling illegal immigration and undercutting businesses which play by the rules."
The restaurants have been served with penalty notices for employing the illegal workers.