CHICAGO (AFP) - A toddler and a man were fatally shot while riding in a car in Chicago, in a Valentine's Day attack captured in a live video on Facebook.

Police said on Wednesday (Feb 15) that they were still searching for a suspect in the shooting, which shocked a city already grappling with a surge in violence so severe that it has drawn the condemnation of President Donald Trump.

The two-year-old boy, identified by US media as Lavontay White, was shot in the head on Tuesday and died later at a hospital.

The boy was riding in the back seat of a car, with his 20-year-old aunt in the front passenger seat and a 26-year-old man driving, according to authorities, when another man began shooting at them.

Police said the pair were live-streaming their car ride on Facebook Live as shots rang out.

The driver, who also died of a gunshot wound to the head, was the intended target of the gang-related shooting, police said.

The woman, who was reportedly pregnant, was wounded in the stomach and survived.

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"This has just got to stop somewhere," police chief Eddie Johnson told news media on Tuesday, struggling to contain his frustration.

"Our children shouldn't have to keep paying the price for our inability to hold repeat gun offenders accountable for their actions," Johnson said.

"I'm sick of it, and I know Chicago is sick of it."

Johnson has repeatedly blamed lax sentencing of repeat gun offenders as a major reason why police struggle to stem the Midwestern city's raging violence, which authorities have attributed largely to gangs.

Last year, there were more than 750 murders and 3,500 shootings - levels not seen in Chicago in two decades.

President Trump has repeatedly criticised Chicago's violence, and tweeted that he would "send in the feds" if the city did not fix the problem.

Chicago Mayor Rahm Emanuel has said he would welcome federal help and additional funding to complement the efforts of local law enforcement.