A man is in custody after a tense stand-off inside a brothel.

Police were called to the business in Arndell Park in Sydney’s west just after 2pm Sunday after reports a man was armed with a gun.

PolAir, the Public Order and Riot Squad and the Tactical Operations Unit were called in when the 29-year-old allegedly refused to leave the building.

Know the news with the 7NEWS app: Download today

Nearby roads were closed and workers evacuated from the premises as a precaution.

Just before 8.45pm, the man was arrested and a replica gun was seized.

He was treated for minor injuries before being taken to hospital under police guard.

A crime scene remains in place and investigations are ongoing.