Humberside Police said the woman involved in the incident went into a house on Portland Place, in Grimsby, North-East Lincolnshire.
A spokesman said specialist officers, including negotiators, have been deployed at the scene on Saturday afternoon.
He said: “Officers are currently in attendance in the Portland Place area of Grimsby, off Weelsby Road, following reports of a woman brandishing a firearm in the street.
“The woman is now inside an address on Portland Place and road closures and a police cordon have been put in place to protect the public and ensure the safety of all involved.
“Specially trained police officers including negotiators have been sent to the area to support community officers.”
He urged members of the public to stay away from the area until the situation is resolved.