A man has been arrested after allegedly making a threatening gesture outside a place of worship in Sydney's north-east.

Police were called to a place of worship on Yeo Street in Cremorne about 9.55am after a man was allegedly spotted pointing what was believed to be a firearm from a moving truck towards the building.

The two men were then arrested on Raglan Street in Mosman about 11.30am.

The 23-year-old passenger was taken to Chatswood Police Station, where he is assisting with inquiries.

The 21-year-old driver was released and pending further inquiries.

Officers attached to Raptor, the Dog Unit and Traffic and Highway Patrol assisted in the search for the firearm, however, it was unable to be located.

Investigations are continuing.

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