One person was killed and children were among the 21 injured after a mass shooting at the Kansas City Chiefs’ Super Bowl victory parade triggered panic among huge crowds of fans.

Shots rang out on Wednesday in Kansas City in the United States moments after jubilant Chiefs players addressed a vast, cheering crowd, sending shocked fans fleeing in a tragic end to what had been a joyous morning of celebrating the NFL champions.

Police said three people had been taken into custody after the attack near Union Station, but the motive behind the shooting was still under investigation.

Fire department chief Ross Grundyson told a news conference that many of the victims had suffered “life-threatening injuries”.

A local DJ, Lisa Lopez, was killed in the assault, her radio station said.

The authorities said more than one million people were expected for the parade, which was held in unseasonably sunny, warm conditions in central Kansas City.

Mass shootings are common in the US, where there are more guns than people and about a third of adults own a firearm.

The attack in Kansas City was not the only shooting to grab national headlines on Wednesday. Four students were also shot outside a high school in Atlanta, while three police officers were shot during a standoff in the national capital Washington, DC. All are expected to survive, according to media reports.

The shootings came six years to the day after 17 people were killed in an attack at a high school in Parkland, Florida.

Polls show a majority of Americans favour stricter gun regulations, but the powerful firearms lobby and mobilised voters supporting the country’s culture of strong gun rights have repeatedly stymied lawmakers from acting.