Cash earmarked for tsunami reconstruction work was diverted to unrelated projects, a Japanese government audit showed as residents of the devastated northeast voiced frustration over the slow pace of rebuilding.

Parts of the 14.9 trillion yen ($187 billion) were used to fund an array of unconnected works, including road-building on the southern island of Okinawa and handouts to help firms not based in the disaster zone, press reports have said.

They also included 8 billion yen for the purchase of rare earths, key components for high-tech products such as electric cars and smartphones, and 4.2 billion yen used to send disaster-prevention equipment to Southeast Asian countries.

The March 2011 earthquake-triggered tsunami killed nearly 19,000 people in Japan's worst peace-time disaster, which also left it grappling with a nuclear emergency at Fukushima.

Nearly 20 months on more than 300,000 people are still living in temporary homes, either because they have been unable to rebuild after the tsunami or because radiation levels around the nuclear plant mean it is unsafe to return.

Politicians from the devastated northeast repeatedly express exasperation at the slow pace of reconstruction and a lack of leadership from Tokyo.

"We residents in the disaster-hit area hope the reconstruction budget will be used primarily for rebuilding our communities," said Chizuo Hayashi, an official at the reconstruction bureau of Fukushima prefectural government told AFP Thursday.

The figures came in a government-commissioned 141-page audit released last week detailing 192 public projects purportedly aimed at reconstruction and disaster prevention.

"The purpose of the report is to expose to the eyes of the public details of the budgeted projects," board of audit official Tetsuya Hosokawa said Thursday.

"We didn't say which projects were appropriate and which were not, but following criticism by media and the public, each ministry may review their budgeted projects," he said.

Reconstruction minister Tatsuo Hirano said earlier this month "we are reviewing this year's projects on the premise that suspension of budget use is possible".

The audit revelations are reminiscent of the worst years of Japan's pork-barrel politics that observers say have left the countryside littered with useless bridges and barely-used roads that go nowhere.