Rescue operations are underway to rescue 400 people who are stranded due to flooding and landslides, according to a statement by the town's prefecture disaster prevention office.
Over 1,100 people were evacuated from their homes and are taking shelter in public facilities across Iwaizumi, the statement says.
Prefectural officials confirmed that nine bodies were found in the Ran Ran retirement home after the nearby Omoto river broke its banks. Police are working to identify the bodies.
Another home for the elderly, Friendly Iwaizumi, avoided casualties as staff were able to move residents to the second floor of the building and avoid the floodwaters. Ran Ran is a single-storey structure.
The body of one other man, in his 70s, was discovered elsewhere in the prefecture. Four people are still missing, and around 700 people are stranded, according to a statement from the prefectural government.
Lionrock descended upon northeastern Japan just a week after Typhoons Mindulle and Kompasu pummeled Japan.
The typhoon passed Japan overnight and turned to a low pressure system. Heavy rain produced by the system flooded areas of the northernmost island of Hokkaido, causing evacuations and riverbank collapses.
The Sorachi River, near the town of Minami Furano broke its banks, cutting off access to the town.
One man is missing after a car he was traveling in was taken by floodwaters. Two other people traveling in the car were able to escape to safety.
Over 4,200 residents have been ordered to evacuate, while 26,000 have been are advised to do so.
Heavy rain fell in areas of northeast China ahead of the system's arrival on the mainland.
Hunchun City in Jilin Province, which had previously experienced a drought. The dry conditions exacerbated the risk of flooding, Chen Tie, director, Hunchun Water Conservancy Bureau, told CNN affiliate CCTV.
"Hunchun had suffered from a drought before the sudden (downpour) of more than 100 millimeters last night. At first it failed to cause much damage because dry land absorbed the rainwater, but the soil has already got saturated overnight," Chen said.
"Consequently we will face enormous pressure to prevent flood if the rain continues."