Officers were called to the scene about 6.30pm that night with reports of a fight between two men, who were known to one another, on Main Street.

Detective Acting Inspector Rob King said several good Samaritans had attempted to provide first aid to the now-deceased 65-year-old man from Fingal Valley.

"A male was said to be unconscious and unresponsive," Acting Inspector King said.

"Members of the public, including a volunteer ambulance officer, responded to that and provided CPR until other emergency services arrived.

"Unfortunately, the unconscious male later died as a result of injuries believed to be sustained through that incident.

"It's obviously a very sad situation and has a severe impact on such a small community."

The second man - also a Fingal Valley resident - allegedly involved in the fight was found by police a short time later, and was willingly taken into custody.

Acting Inspector King said investigations into the incident were still ongoing, and as such could not comment on the nature of injuries sustained by the dead man, or if weapons were involved in the fight.

The inspector said police could not say what led to the fight, however he did say the man in custody did not receive injuries requiring hospital treatment.

Acting Inspector King said the second man, who remained cooperative, was yet to be formally interviewed by detectives and charges had not been laid.

Anybody who could assist with the investigation was urged by the inspector to contact police.

"The incident occurred about 6.30pm," Acting Inspector King said.

"At that particular time, there were members of the public in the area, a number of whom witnessed the incident.

"We would like to speak to those people that saw something."

Information can be provided to police by phoning 131 444, or by contacting Crime Stoppers Tasmania on 1800 333 000.

EARLIER:

Police say a man is dead and another in custody after what they describe as an "altercation" in an East Coast town.

A statement released by police said officers were informed of a fight between two men at Main Street, St Marys about 6.30pm on Tuesday, March 26.

Police said one man was injured and ultimately died, while the second was taken into custody and was assisting investigators with their inquiries.

A stretch of the road, between Franks Street and The Flat, was closed for several hours as officers remained at the scene.

Diversions via Elephant Pass were in place until about 1.40am on Wednesday, March 27 when the police reported the road was reopened.

As of 7.30am that day no further updates about the man taken into custody had been provided.

Police thanked the public for their patience and cooperation while they carried out their investigations.