FRESNO (AP) — Two adults and two children were killed in an apparent murder-suicide Sunday at an apartment building in California's Central Valley, while a fifth person was hospitalized in critical condition, police said.

Police were called to investigate a disturbance at the Fresno home shortly before 7 a.m. They found a man outside the apartment suffering from a stab wound, The Fresno Bee reported.

Capt. Dennis Bridges told the newspaper that officers then heard a single gunshot. When they went inside the apartment, they found a woman believed to be in her 20s with a self-inflicted gunshot wound and a man in his 20s or 30s dead of a gunshot wound.

Two children — an 18-month-old and a 3-year-old — also died from gunshot wounds.

"We're investigating to determine exactly how the children and the adult male died and the circumstances around the man suffering from a stab wound," Bridges said. He did not know if there was a history of domestic violence calls or other disturbances at the apartment.

The man suffering from the stab wound was taken to a local hospital, where he was reported to be in critical condition.

A neighbor, Eric Gonzalez, described the residents of the apartment as a "normal" family.

"I never saw them fighting. They would come out with the baby carriage, and the man was taking care of his children," he told an Associated Press reporter outside the apartment complex.

Gonzalez said he did not hear any fighting or gunshots before the incident.

Police didn't immediately return calls from the AP seeking additional information.