Eight people were killed and others injured in separate shootings that took place Monday in three US states, according to police and local sources.
Four people were killed and three others were seriously injured in two shooting incidents in a northern California region, according to US media reported Monday.
The San Mateo County Sheriff announced on Twitter that police had rushed to "the site of a mass shooting" and that a suspect had been arrested.
Local television channels affiliated with NBC and IBC reported four deaths in two different locations.
Prior to this announcement, police in the US state of Chicago reported that two people were killed and three others seriously injured in an armed attack on a residential apartment in the state on Monday.
The police explained that the victims were killed in a shooting in an apartment located in the South Shore neighborhood.
She said that the attack appeared to be deliberate and not a random act, noting that several suspects fled after the shooting and none of them were detained.
While it is not yet clear the motive behind the shooting.
Hours earlier, US media reported that two students had been killed and a teacher injured in a shooting at a school in Dimoan, Iowa.
The United States frequently witnesses shootings and other violence related to firearms, whose possession and carrying laws are among the most lenient in the world.