The high-capacity magazines found in the gunman's possession indicated he could have fired 250 rounds

Investigators have so far found no evidence to indicate that a mass killing in the US city of Dayton was motivated by racial hatred, the police said on Monday.

"Just based on where we're at now we are not seeing any indication of race being a motive," Dayton police chief Richard Biehl said as he gave an update into the investigation into the shooting in the early hours of Sunday.

Six of the nine victims killed by the 24-year-old white gunman were black, and Biehl said it was too early to rule out a racial motive for the attack.

"We are not through all the evidence and so until we're through all the evidence we cannot rule that out," Biehl told a news conference.

One of the gunman's victims was his own sister.

W had police not shot him dead in less than a minute.

He said that level of firepower in the hands of an unregulated civilian was "fundamentally problematic."

Among the 30 or so people wounded in the shooting spree, 14 had been hit by bullets, including a friend of the killer's sister who was hit in the torso. The friend was helping police in their inquiries, Biehl said.

The three young people had arrived together in the historic Oregon area of the city, home to numerous bars, nightclubs and restaurants, but the shooter separated from the others, Biehl said.

The shooting happened 13 hours after another gunman opened fire on crowds in a crowded Walmart supermarket in El Paso, Texas, on Saturday morning, killing 21 people after posting an anti-immigrant screed online.

The El Paso shooter was arrested and charged with homicide and could face the death penalty.

Mexico's foreign minister described the shooting, in which seven Mexicans died, as a "terrorist act" and said the country may consider demanding extradition of the gunman.