In the aftermath of the devastating March tsunami, Japan's underworld made a rare display of philanthropy, handing out emergency supplies to survivors, sometimes days before aid agencies arrived.

Three months later, however, the yakuza appears to have dispensed with largesse and is instead hoping to cash in on the daunting clean-up effort in dozens of ruined towns and villages.

The government and police fear they are losing the battle to prevent crime syndicates from winning lucrative contracts to remove millions of tonnes of debris left in the tsunami's wake, including contaminated rubble near the Fukushima Daiichi nuclear power plant that many firms are reluctant to handle.

The disaster created almost 24m tonnes of debris in the three hardest-hit prefectures, Fukushima, Miyagi and Iwate, according to the environment ministry. So far, just over 5m tonnes – or 22% – has been removed.

Those lining up to profit from the clearance operation, which is expected to take three years, include homegrown gangs and Chinese crime syndicates, according to the June edition of Sentaku, a respected political and economic affairs magazine.

The magazine recounts the story of a leading Chinese gangster who, accompanied by a national politician, visited the mayor of Minamisoma – a town near Fukushima Daiichi, where a partial evacuation order is in place – hoping to win contracts to remove radioactive waste that, according to police, could have ended up at disposal sites in China.

The man, named in the article as Mr X, had reportedly ingratiated himself with the local authorities by handing out free food to people living in evacuation centres.

The mayor had no knowledge of the man's underworld connections, the magazine said.

"If they help citizens, it's hard for the police to say anything bad," said Tomohiko Suzuki, a journalist who has written several books on the Japanese underworld.

"The yakuza are trying to position themselves to gain contracts for their construction companies for the massive rebuilding that will come."

An unnamed senior gangster countered in the Weekly Taishuu magazine: "It takes too long for the arm of the government to reach out here so it's important to do it now. Our honest sentiment right now is to be of some use to people."

In the days after the tsunami, the wealthiest yakuza gangs reportedly sent dozens of trucks loaded with water, nappies, instant noodles, blankets and other supplies worth an estimated half a million dollars to the stricken region.

The race to profit from the operation to remove what is left of wrecked buildings and gain a share of the reconstruction budget is expected to intensify in the coming months.

Officials have said that the removal of debris should come under central government control, and the names of "antisocial" individuals have been forwarded to local authorities.

But given the sheer quantity of debris, and the manpower required to remove and dispose of it, few believe Japan's most powerful yakuza gangs will be kept out altogether.

The police's job has been complicated by the emergence of yakuza front companies that, without time-consuming investigations, are impossible to distinguish from legitimate businesses.

As Sentaku notes: "It appears to be an uphill battle to prevent the yakuza and other crime syndicates from benefiting from the multitrillion-yen reconstruction projects."

Traditionally, construction has been a dependable well of cash from which the yakuza, with an estimated nationwide membership of 80,000, has supped long and often.

"The nexus of massive construction projects, bureaucrats, politicians, businessmen and yakuza are as revealing about Japan as they are about Italy and Russia," Jeff Kingston, director of Asian studies at Temple University in Tokyo, wrote in his recent book, Contemporary Japan.

"In Japan, the yakuza cut on construction projects is estimated at 3%, a vast sum that keeps them afloat, given that during the 1990s the public works budget was on par with the US Pentagon's budget and remains quite high despite huge cutbacks."

It is not the first time the yakuza has revealed its usually well-hidden philanthropic side.

After the western port city of Kobe was struck by an earthquake in January 1995, members of the locally based Yamaguchi-gumi, Japan's biggest crime syndicate, were among the first to hand out food and water to survivors.