An unknown number of creatures were on the loose in the snow-covered Hachimantai bear park in Akita prefecture, which keeps 38 animals, most of them brown bears.
By early evening, local hunters had shot dead six of the animals, all within the gated park campus, and had recovered two bodies, thought to be those of workers at the facility, an Akita police spokesman said.
Emergency services were alerted after 10am (0100 GMT) to bear attacks in the park, which was closed to tourists for the winter.
Of the three staff who were there at the time, one man managed to escape, but one woman was known to have been badly mauled and another went missing.
Emergency workers later recovered two bodies, the police spokesman said, with local media reports saying they were those of the two female workers.
The police spokesman said the incident was not yet over.
"It's difficult to say exactly how many bears left their cages," he said, stressing that emergency workers were scrambling to contain the situation.
It took several hours before emergency workers could even go into the bear park for fears of being attacked by bears on the loose.
Police have asked local residents and school children to stay indoors.
During warmer months, tourists visit the park where they are permitted to feed the animals.
AFP