A formal identification process is underway, police said, however it has been reported the man was a Russian fisherman. A motel close to where he was found has been cordoned off, Fairfax reported.
Earlier today the inspection was believed to be a homicide investigation, instead the death is being treated as "unexplained", Detective Senior Sergeant Jason Stewart said.
"Police are aware of speculation in the community, however the investigation is still in its early stages and further information will be released in due course," he said.
"Police are currently speaking to a number of people and are not actively seeking anyone else in relation to the death."
A scene examination is currently underway and a post-mortem is yet to be completed, he said.
A witness spotted "10 or more" police cars near the park and outside a strip of shops on Ferry Rd about 3.30am.
Most of the park was cordoned off, he said, and several police dogs were in the area.
"The dogs were definitely part of whatever was going on in the park," he said.
Transport for Christchurch said Ferry Rd had now been opened to two-way traffic.
Anyone who was in the area around Edmonds Park between 2am and 3.30am is asked to contact police at their nearest station, or anonymously contact Crimestoppers on 0800 555 111.