Five people, including four members of a family, were shot dead inside a house in Lerdo, a city in the northern Mexican state of Durango, officials said.

A 9-year-old girl was among the victims, the Durango Attorney General's Office said.

The little girl's brothers, ages 21 and 23, 44-year-old mother and a 43-year-old man were also killed, media reports said.

The killings occurred on Sunday morning, the AG's office said.

Investigators are trying to determine the motive for the murders and find the perpetrators, officials said.

Lerdo is Mexico's second most violent city, trailing only the Pacific resort of Acapulco, with a homicide rate of 110 per 100,000 residents, the Citizens Council for Public Safety and Criminal Justice said in a report. EFE