A gunman shot two Democratic state lawmakers in Minnesota early Saturday, killing one and her husband and wounding the other, in what the northern US state's governor said were politically motivated attacks.

The shootings came at a moment of deep political divisions in the United States, as thousands took to the streets in protest at the policies of Republican President Donald Trump.

The suspected assailant — named in US media reports as 57-year-old Vance Boelter — was still at large, officials said, with a massive manhunt underway.

Trump and US Attorney General Pam Bondi decried what they called "horrific violence" and said  perpetrators would be prosecuted to "the fullest extent of the law."

State representative Melissa Hortman — the former speaker — and her husband Mark were killed at their home in the Minneapolis suburb of Brooklyn Park, Governor Tim Walz told a press conference.

State senator John Hoffman and his wife Yvette were shot and wounded at their home in nearby Champlin, the governor said, his voice breaking with emotion. He said officials remained "cautiously optimistic" they would recover. 

"This was an act of targeted political violence," Walz told reporters. 

"Peaceful discourse is the foundation of our democracy. We don't settle our differences with violence or at gunpoint."

Drew Evans, superintendent of the Minnesota Bureau of Criminal Apprehension, said Hoffman and his wife were shot first, and as police investigated, Hortman and her husband were shot about 90 minutes later. 

The suspected gunman was able to escape during an exchange of gunfire with officers near Hortman's residence, Evans told reporters.

"We're actively searching for that individual right now," he said.

The New York Times, The Minnesota Star Tribune and CBS News, all citing unnamed sources with knowledge of the investigation, named the suspect as Boelter.

Praetorian Guards Security Services, a home security company, describes Boelter on its website as the director of security patrols.

Impersonating law enforcement

In both cases, authorities believe the assailant was impersonating a law enforcement officer.

"The suspect exploited the trust that our uniform is meant to represent," said Bob Jacobson, commissioner of the Minnesota Department of Public Safety.

An anti-Trump rally in Minneapolis — part of the national wave of "No Kings" protests planned for Saturday — was canceled after police issued a shelter-in-place order because of the shootings. 

Flyers for the protests were found in the suspect's car, as well as a manifesto that named numerous politicians and state officials, police said.

Police are looking for a white man with brown hair, wearing black body armor over a blue shirt and blue pants, local TV station KSTP said.

"We do have the suspect's car. Suspect is on foot," said Mark Bruley, the police chief in Brooklyn Park, where Hortman lived.

The United States has been deeply divided since Trump returned to the White House in January.

The Republican president has drawn criticism from Democrats over his harsh deportation policy, his assault on universities and the media and a perceived flouting of limits on executive power as he pushes his agenda.

"At this precipice moment we're on, this tragic act here in Minnesota should serve as a reminder to all of us," Walz said.

"The democracy and the debates in the halls of Congress, in state houses, in school boards, is a way to settle our differences peacefully and move society to a better place."

US Senator Amy Klobuchar of Minnesota remembered Hortman as a friend who entered politics at the same time as her and dedicated her life to serving the state, working on issues such as women's rights and clean energy.

"Let me be absolutely clear: this was an act of targeted political violence, and it was an attack on everything we stand for as a democracy," Klobuchar said in a statement. "We must all condemn it."

Minnesota's other US senator, Tina Smith, also issued a statement condemning the shootings.

Former House member Gabby Giffords, who survived a shooting to the head in 2011 and is now a prominent advocate for the prevention of gun violence, described herself as "devastated" by the death of Hortman. 

"We must protect our democracy from those who try to destroy it with a gun," Giffords wrote on X.