Five Chinese nationals were on Friday morning arrested in Njumbi villas, Lavington, while in possession of security equipment.
The equipment found in their possession included Chinese-made teargas canisters, radios, sound and light sirens, smoke detectors, police uniforms, military bags and boots.
The Director of Immigration Services Mr Alexandar Muteshi said the early morning raid was part of the ongoing crackdown on illegal immigrants.
The raid was conducted by police and immigration officers.
“The raid was conducted at 5am by our officers following a tip off and we are investigating to find out why they were in possession of the equipment,” he told journalists at Nyayo House.
The five Chinese nationals have valid passports, but none had a working permit.
Mr Muteshi said that one of them, who reviously worked at the Standard Gauge Railway, had his work permit cancelled.