Police found both on the ground, not breathing, at the 17-acre Washington Pond condominium complex off Pascack Road and Linwood Avenue just after 8 a.m.
CPR was conducted on both at the scene before they were rushed to The Valley Hospital.
Both from West New York, the men "appeared to be overcome by the fumes of a running lawnmower in the trailer," Detective Heather Castronova said.
OSHA responded, along with township first responders and the Bergen County Sheriff's Bureau of Criminal Identification, which collected evidence.
The trailer belongs to AJR Landscaping of Cresskill.
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