The stench of flesh rotting on a sultry day fills the air as cleaner Hidemitsu Ohshima steps into a tiny Tokyo apartment where a dead man lay decomposing for three weeks.

The man, believed to be in his 50s, died alone in a city he shared with tens of millions of other people but no one noticed, making him the latest victim of kodokushi or "dying alone" -- a growing trend in aging Japan.

Decked out in a white protective suit complete with rubber gloves, Ohshima lifts up a futon mattress soaked with the dead man's bodily fluids, only to uncover a writhing mass of maggots and black bugs.

"Ugh, this is serious," he says. "You wear protective suits to defend yourself from bugs that may or may not be carrying diseases."

Kodokushi is a growing problem in Japan, where 27.7% of the population is aged over 65 and many people are giving up trying to find partners in middle age, opting instead for a solitary existence.

Experts say a combination of uniquely Japanese cultural, social and demographic factors have compounded the problem.

There are no official figures for the number of people dying alone who stay unnoticed for days and weeks but most experts estimate it at 30,000 per year.