Police have charged a Sydney tradesman who they say was building guns for a criminal gang.

Officers from the Middle Eastern Organised Crime Squad arrested the 55-year-old at his home in the city's west at Greystanes yesterday morning.

They say the fitter and turner has been manufacturing and modifying guns, then selling the illegal weapons to an organised crime group.

An ambulance took the man to hospital after he complained of being short of breath.

Police then transferred the man to Merrylands Police Station, where he was charged with 38 offences.

They include charges for the manufacture, possession, conversion and sale of illegal guns.

The man was held in custody overnight to face court today.

Police say yesterday's arrest completes the work of Strike Force Centre, which was set up a year ago to investigate the sale of illegal guns and drugs by a criminal syndicate.