A Japanese woman has been arrested on suspicion of hiding the body of her four-year-old son in a refrigerator for nearly two years, according to police.

Miyuki Otsuka, 33, turned herself in to police in western Hyogo prefecture, and police later found a decomposed body in a plastic bag in her fridge, a police spokesman said.

"We believe it was the body of her son," who was aged four in 2007, the official said, adding that police were conducting a DNA test.

Her husband, who was the child's stepfather, 34-year-old truck driver Ryu Otsuka, was also arrested.

News reports quoted the woman as telling police that her husband had abused the boy and that the child died after being bundled up and put in a box.