A prominent Democratic state lawmaker in Minnesota and her husband have been killed, and another Democratic state lawmaker and his wife were shot, in the early hours of Saturday.

State representative Melissa Hortman has died, as has her husband, Mark, the state’s governor, Tim Walz, confirmed at a press conference on Saturday. He said the shooting “appears to be a politically motivated assassination”. Hortman was the top Democrat in the Minnesota house and the former speaker. The Democratic state senator John Hoffman and his wife, Yvette, were both shot multiple times and are out of surgery, and Walz said he was “cautiously optimistic” both will survive.

The gunman was still at large, law enforcement said on Saturday, and the city of Brooklyn Park was still under a shelter-in-place order. The shooter was impersonating a police officer, dressed in a uniform that would appear to be real to most people, police said. Sources told the Associated Press that 57-year old Vance Boelter is currently being sought as a suspect.

“No Kings” protests against the Trump administration are set for midday at the Minnesota state capitol and around the country, but the Minnesota state patrol and Walz have asked the state’s public not to attend “out of an abundance of caution”. The state patrol said “No Kings” flyers had been found inside the suspect’s vehicle.

Organizers said they would cancel events across the state that hadn’t already started, though the main protest at the state capitol in St Paul is under way, with people in attendance.

Brooklyn Park’s police chief, Mark Bruley, said at a press conference that the suspect drove a vehicle that looked identical to an SUV police squad car. “It was equipped with lights, emergency lights, that looked exactly like a police vehicle, and yes, they were wearing a vest with Taser, other equipment, a badge very similar to mine, that, no question, if they were in this room, you would assume that they are a police officer.”

The man had a list of other lawmakers and officials in the vehicle police searched, and alerts were sent out to take action and provide security to others, Bruley said.

“There was a list of individuals, and the individuals that were targeted in this situation were on that list,” said Drew Evans, the superintendent of the Minnesota bureau of criminal apprehension. He added that it was “far too early in the investigation” to provide a motive or assess whether the victims had been targeted for their political affiliation, but that he believes the state will be able to provide more information on the motivation behind the attacks as the investigation unfolds.

“We’re here today because an unspeakable tragedy has unfolded in Minnesota,” Walz said. “My good friend and colleague, Speaker Melissa Hortman, and her husband, Mark, were shot and killed early this morning in what appears to be a politically motivated assassination. Our state lost a great leader, and I lost the dearest of friends.”

He added that Hortman was “someone who served the people of Minnesota with grace, compassion, humor and a sense of service. She was a formidable public servant, a fixture and a giant in Minnesota. She woke up every day determined to make this state a better place. She is irreplaceable.”

Democratic state senator John Hoffman and his wife, Yvette, were both shot multiple times and are out of surgery, and Walz said he was “cautiously optimistic” both will survive.

“This was an act of targeted political violence,” Walz said. “Peaceful discourse is the foundation of our democracy. We don’t settle our differences with violence or at gunpoint.”

At about 2am local time, police received a call in Champlin, a suburb of Minneapolis, that Hoffman and his wife had been shot, Evans said. Police in Champlin responded to that location, and police in a nearby suburb, Brooklyn Park, assisted.

Police in Brooklyn Park went to Hortman’s house at about 3.30am to check on her, given the nearby shooting of Hoffman. Upon arrival at Hortman’s house, officers saw a supposed police vehicle in the driveway with emergency lights on and what appeared to be an officer coming out of the house, Bruley said. The gunman, impersonating an officer, immediately fired at them, and then was able to escape out the back of the house, Bruley said.

“This is somebody that clearly had been impersonating a police officer, again, using the trust of this badge and this uniform to manipulate their way into the home,” Bruley said.

Police found a man with gunshot wounds, Hortman’s husband, and administered first aid, but he was pronounced dead shortly after. Officers then used a drone to identify the woman, Hortman, in the home.

Bruley advised people in the area to call in to the police department if an officer arrives to ensure the officer belongs there, which dispatch would be able to confirm. Officers were approaching people in pairs of two officers as the search continued, he said, so if there is a single officer outside your door, do not answer. Police had detained several people for questioning, but did not have anyone in custody at the time, Bruley said.

Bob Jacobson, the commissioner of the state’s department of public safety, said there was increased security in place for elected officials and others who may be at risk.

“This is a dark day today for Minnesota and for democracy,” Jacobson said. “We will not allow fear or violence to define who we are or how we move forward. We will stand together. We will stand strong … These are public servants, leaders who committed their lives to improving the lives of others, and they were targeted in a violent and cowardly way.”

Minnesota’s house of representatives was evenly split between Republicans and Democrats. Democrats have a one-vote majority in the state senate.

Amy Klobuchar, the state’s Democratic senator, called the shootings “a stunning act of violence”: “My prayers are with the Hortman and Hoffman families. Both legislators are close friends and devoted to their families and public service.”

Trump said in a statement that he had been briefed on the shootings, which appeared to be a “targeted attack against state lawmakers”. The US attorney general, Pam Bondi, and the FBI was investigating and would prosecute anyone involved “to the fullest extent of the law”, Trump said. “Such horrific violence will not be tolerated in the United States of America,” he said. “God bless the great people of Minnesota, a truly great place!”

The shootings took place at a time when political violence has become more commonplace in the US, though the vast majority of Americans do not support it, according to a University of Chicago survey.