Americans have given nearly three-quarters of a billion dollars in private donations to help tsunami-wracked communities, a report said, as Japan marked the second anniversary of the disaster on Monday.

Individuals, companies and non-profit groups have donated $712.6 million to help crisis-stricken areas over the last 24 months, the Japan Center for International Exchange said in a report released last week.

The private sector total is the largest ever given to a developed country and the third biggest disaster donation after those for the 2004 Indian Ocean tsunami and the 2010 quake in Haiti, it said.

The largest donor was the American Red Cross, which gave $312 million, followed by Save the Children, USA, which raised $26.15 million, it said.

Japan is marking the second anniversary of the ferocious tsunami, which left nearly 19,000 people dead or missing, and sparked the worst nuclear accident in a generation.

Efforts to rebuild the disaster-hit region have been slow; figures show 315,196 people are still without a permanent home, many in cramped temporary housing units.