Homicide detectives are at Dandenong Park on Pultney Street where the man's body was found, just 200 metres from the local police station, about 4.30am.

An off-duty Protective Service Officer happened upon the man's body while walking his dog, police said.

The man, believed to be aged in his 40s, was found with upper body injuries and police are treating his death as suspicious.

However, the man's identity is yet to be confirmed.

Deputy Commissioner Graham Ashton could not detail the nature of the man's injuries, but said initial investigations suggested the victim died in the park.

"We have certainly concluded that obviously [there are] suspicious circumstances around his death," he told reporters on Wednesday.

Police have blocked off a large section of the park around the Dandenong Croquet Club, near the intersection of Pultney and Power streets.

Mr Ashton said part of the nearby court precinct had also been cordoned off and asked the public for patience as investigations continued.

He said police would likely remain at the scene for the remainder of the day.

State Emergency Service volunteers with the Greater Dandenong unit are also at the scene, searching the parkland for items of interest.

Meanwhile, police are awaiting the results of toxicology tests on a man whose body was found on a St Kilda street on Tuesday.

Mr Ashton said there were no obvious signs of injury to the man's body, forcing police to wait for the results of the medical examination before taking their investigations further.

Anyone with information is asked to contact Crime Stoppers on 1800 333 000.