Police say a 54-year-old man is dead after a overnight standoff with police, following the discovery of guns at a property.

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In a statement this morning, Police Commissioner Mike Bush said a search warrant was issued yesterday at a St Martins address where police found a number of firearms.

Police then sought a 54-year-old man over the guns, but he died during a subsequent standoff with police.

Police located the man inside a stopped vehicle in the Richmond Park area about 12.30am today, but he refused to get out of his vehicle.

A police negotiation team spoke with him over a number of hours, and a police helicopter was called in, as well as Armed Offender Squad members.

About 3.40am, police approached the vehicle and found that the man was critically injured with what looked to be a stab wound - a knife was found in the vehicle.

Members of the public reported hearing gunshots, but police said that was the sound of gas canisters being deployed.

Mr Bush said a high priority investigation is underway to find out whether or not this man posed a threat to the community.

Further searches of properties and interviews with family and associates will be carried out.

Mr Bush said that, at this time, there is no evidence to suggest the man was connected to the March 15 terrorist attack, but that they are looking at any potential link.

Police will remain in the area of Richmond Park and St Martins as scene examinations continue.