Three members of a family were slain early on Friday at a state park campsite in Iowa, and the man suspected of killing them was found dead nearby from an apparently self-inflicted gunshot wound, authorities said.

Police were alerted at 6:20 a.m., about 30 minutes after sunrise, to a triple homicide at the Maquoketa Caves State Park campground, about 180 miles northeast of Des Moines, the state capital, according to the Iowa Department of Public Safety (DPS).

Officers arriving at the scene discovered bodies of the three victims and a lone survivor who was unhurt before looking for a fifth camper who was unaccounted for, said Mitch Mortvedt, a spokesperson for the DPS division of criminal investigation.

Police did not say how the three were killed, but Governor Kim Reynolds referred to the incident as a shooting.

A search of the vicinity led officers to the body of the man they believed was the killer, Anthony Orlando Sherwin, 23, just west of the park, the agency said in a statement.

The names of the victims and the survivor were being kept confidential pending notification of next of kin, but all four were believed to be members of the same family, Mortvedt said. The suspect was not related to them, he added.

The killings were believed to have occurred shortly before a camper from an adjoining site placed the emergency-911 call that first notified authorities, Mortvedt told Reuters by phone.

No further information was immediately available about the slayings, including a possible motive or even the cause or means of the victims' deaths, Mortvedt said, adding that besides the gun he used to take his own life, the suspect was "known to have had a sharp-edged weapon."

Reynolds issued a statement saying she was "horrified by the shooting" and "devastated by the loss of three innocent lives."

The Maquoketa Caves State Park, part of which is listed on the National Registry of Historic Places, was closed until further notice, the safety department said.

The park features massive bluffs, with trails that wind through geologic formations and caves that can be explored by hikers and spelunkers.