The suspected gunman appeared to have taken his own life after the shooting spree, a ministry official said.
Jason Tarkong, a public safety spokesman, said that among those killed in Friday's rampage were a four-year-old boy and a two-year-old girl.
Officials said the shootings occurred in two different areas of the island, starting with a popular tourist spot where the man fired a barrage of bullets from his van at the South Koreans.
He then then drove to a shooting range where he killed two men and the two children, officials said,
Saipan is the largest island in the US Commonwealth of the Northern Mariana Islands in the West Pacific. It has a population of about 62,000.