Four people were shot and killed at a bar in Anaconda, Mont., on Friday, prompting an escalating manhunt for the suspect across the mostly rural foothills of central Montana.

The gunman opened fire in the Owl Bar around 10:30 a.m., a spokesman for the Montana attorney general said in a statement. The suspect “is believed to be armed” in an area west of Anaconda, said the spokesman, Chase Scheuer.

Local, state and federal law enforcement agencies fanned out across the region, with the local police department warning in a social media post that the suspect was “believed to be armed and dangerous.”

The authorities identified the suspect as Michael Paul Brown and warned residents to avoid the Stumptown area, where he was last seen in a white Ford pickup.

The sheriff’s office in neighboring Granite County said on social media that a police tactical team had searched a house looking for the suspect, but had not found him. Businesses nearby were on lockdown, along with the county school district offices.

Gov. Greg Gianforte of Montana posted on social media that he was monitoring the situation closely and praying for the victims. The Denver office of the Bureau of Alcohol, Tobacco, Firearms and Explosives said it was sending agents to assist the police in Anaconda.

This is a developing story. Check back for updates.