TOKYO (AFP) - Police in Japan are probing a possible family suicide after a mother and her three young children plunged to their death from an apartment complex.

The bodies of the 35-year-old woman and three youngsters - a seven-year-old boy, a girl aged six, and a two-year-old boy - were found near the entrance of the 14-storey building in Chiba, east of Tokyo, a police spokesman said.

"They are believed to be a mother and her children," he said.

Asked if it appeared to be a forced family suicide, he said: "Police are investigating the case with that possibility under consideration."

The Yomiuri Shimbun daily said the mother's body was found on the ground, with the two older children on top of the entrance roof, while the two-year-old was found stuck in branches of a nearby tree.

Despite a high-quality healthcare system universally available, relatively few people with psychological problems seek treatment in Japan, where mental illness retains its stigma.