Police are investigating a deadly shooting at an elementary school in Bend, Oregon, where a 16-year-old opened fire on Thursday, killing three children and a teacher, before being shot dead by an armed bystander.

Authorities in Oregon said that the three children killed at Silver Rail elementary school were aged five, eight and 11, and that a seven-year-old child and a 54-year-old teacher were also hospitalized with critical injuries.

Officials said on Thursday that the gunman was a 16-year-old resident of Bend and that he forced his way into the school at around 1pm by shooting at locked doors.

As of Friday morning, authorities have not named the victims, the shooter or the bystander who shot and killed him. Bend Police said that the families of the victims had all been notified.

The Bend police chief, Mike Krantz, said on Thursday that the police received an emergency call at 12.59pm on Thursday from a person “in a vehicle who reported being shot at multiple times by a person with a long gun”.

Within minutes, he said authorities received “dozens of 911 calls” reporting that a “shooter had entered the building at Silver Rail elementary school”.

He said that the school went into lockdown at 1.01pm and that at 1.02pm, the first officers arrived on scene.

“Moments later, an officer reported that the suspect had been shot by a community member who had seen the suspect enter the school and pursued him into the school and engaged him.” Krantz said, adding: “our officers entered the building and confirmed the suspect was dead.

“They cleared the school to ensure there were no additional threats and then rendered emergency aid to the victims,” he said. Officers at the scene then subsequently located “five people who had succumbed to their injuries, including the suspect”.

“This is going to be a long investigation,” he said, adding that the police would maintain a large presence at the school for the next few days.

“There are not really any words I can say to any of you that will make this better,” Krantz said. “But please know that we are working hard to ensure that we conduct a thorough investigation.”

The FBI director, Kash Patel, said on Thursday that the FBI’s local office is on the scene and assisting local law enforcement with the investigation.

The Associated Press reported on Friday, citing a law enforcement official briefed on the shooting who spoke on the condition of anonymity, that the shooter used a pump-action shotgun purchased by his mother.

At the news conference on Thursday, the mayor of Bend, Melanie Kebler, said: “Like so many in our community, I’m struggling to make sense of a loss that feels unimaginable.”

Oregon’s governor, Tina Kotek, also attended the conference.

“My heart is absolutely broken today, and our hearts will stay broken in the days and weeks ahead, and my daily prayers will be with this community, with the children, with the parents, and with the educators,” she said.

“All Oregonians mourn this loss today,” Kotek added. “This is a horrible day.”

She also praised the person who “heroically intervened to stop further loss of life”.

“Your actions carry a heavy emotional burden, and I just want you to know that my thoughts are with you as well,” she said.

The city of Bend, home to arbout 100,000 residents, held a candlelit vigil on Thursday night. Hundreds of people gathered in gathered in Bend’s Drake Park as the sun set. Both Kotek and Kebler attended the vigil.

“There is power and love in this park tonight,” Kotek said. “On behalf of everyone who lives in Oregon, I am so sorry for what you are experiencing today. No parent, no family, no community should have to have this kind of day.”

All schools in Bend and La Pine, a neighboring city, are closed on Friday.

In a statement, Steven Cook, the superintendent of Bend-La Pine schools, said: “We are stunned and heartbroken by this senseless tragedy.

“We extend our deepest sympathy to the families and to everyone affected by this violence,” Cook said. “No words can adequately express the grief our community is experiencing.”

The US education secretary, Linda McMahon, also expressed her condolences in a social media post on Thursday, saying that she was “heartbroken by the horrific shooting” and that her “prayers are with the students, faculty, their families, and the entire community”.