A shooter opened fire at Silver Rail Elementary before being shot dead and three children and one adult were killed, CNN and CBS News reported.
Law enforcement officials said the death toll was preliminary and could change.
Police in Bend, a city of about 100,000 residents in central Oregon, said the first call they received "indicated that an unknown man had shot into a car" at Silver Rail Elementary.
Police officers arriving seconds later found the suspect had been shot dead, possibly by a bystander, police said in a statement.
Sheila Miller, a spokesperson for the Bend Police Department, told reporters investigators had yet to confirm who shot the suspect.
Miller told reporters at least two victims were transported to a hospital but she was unaware of their condition.
The subsequent police statement, posted online, said, authorities "have confirmed there were multiple victims," with at least two taken to hospital, adding, "children are among the victims."
Police were on campus within minutes at which time the shooter went down almost immediately, she said.
Silver Rail Elementary was under lockdown, the Bend-La Pine school district wrote on Facebook.
"We're in the process at this time of going room by room and evacuating each of the people who are in that school. ... This is the kind of thing we never want to see happen in Bend. It's devastating," Miller said.
Silver Rail Elementary School serves grades kindergarten through fifth grade, roughly ages five to 11. It has about 450 students and 40 staff members.
with AP
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