One of Japan's largest organised crime syndicates has launched its own website - which urges visitors to stay off drugs.

The website was set up by members of the Yamaguchi-gumi, part of the Japanese mafia, which is known as Yakuza and is involved in activities ranging from prostitution to extortion and white-collar crime.

The site features a corporate song, as well as videos and pictures of Yamaguchi-gumi members - including shots of them helping victims of the Fukushima earthquake.

Experts believe the website is an attempt to restore the standing of the Japanese mafia, whose membership has fallen considerably in recent months due to a poor public image and national economic problems.

Jake Adelstein, a journalist and author who has written extensively on organised crime in Japan, said the Yamaguchi-gumi's online offering is designed to prove its credentials as a humanitarian organisation.

"By presenting an anti-drugs theme, it shows concern for social welfare [and] it shows pictures of the group doing emergency relief after the [Fukushima] and Kobe earthquakes," he said.

"The yakuza motto is 'help the weak and fight the strong.' In practice, it's usually the reverse."

Police officials said they could not immediately confirm wether the website was made by the Yamaguchi-gumi, nor comment on it.

In 2013 the Yamaguchi-gumi started publishing a magazine for members that includes a poetry page, senior gangsters' fishing diaries and a message from the boss.

Part of the fabric of society

Members of the umbrella Yakuza organisation can be divided into three principal categories: tekiya (street peddlers), bakuto(gamblers), and gurentai (hoodlums). The peddlers and gamblers trace their roots back to the 18th century while the hoodlums came into existence after World War II, following the increasing demand for black market goods.

The Yakuza are not illegal and each of the designated groups have their own headquarters, with senior members handing out business cards.

Yakuza members have also a large presence in the Japanese media and operate internationally with more than 100, 000 members.