US officials admitted Thursday that Washington had been over ambitious in its plans to help Haiti in the aftermath of a devastating earthquake, despite pledging about $4 billion in aid.

Five years after the 7.0 quake levelled much of the capital Port-au-Prince on January 12, 2010 more than a million survivors left homeless have been rehoused.

But thousands still live in canvas makeshift shelters as Haiti's own efforts to get back on its feet have been hampered by political instability and by a cholera outbreak blamed on UN peacekeepers' poor hygiene.

US officials said there had been a lot of progress made in health and security, as well as in encouraging economic growth and "incredible gains in the agricultural sector" with yields in some crops up 300 percent.

But a senior State Department official told reporters "the US government was very ambitious in terms of what we expected to accomplish as far as the shelter sector is concerned."

"We had expected many more donors to come forward to partner with us to build new homes, new settlements. And those funds did not materialize," he said.

Even before the quake hit, there had been a 500,000 unit housing shortage in the capital, a gap which on its own would have cost $15 billion to fill. The total amount of international aid pledged for Haiti between 2010 and 2020 was $16 billion.

"So, I think you can understand the resources really aren't there to do everything."

"We realized that we are certainly not going to be able to come anywhere close to building the kind of housing stock that Haiti requires," the official added.

Now the US administration is working with the Haitian government to help Haitians build homes, shifting its focus on housing finance and unlocking funds from financial institutions.

With the impoverished Caribbean nation also mired in a political crisis, another official admitted that in democracy building "we haven't been as successful, quite frankly, because a lot of that depends on the government of Haiti taking certain actions."

"We were I think greatly optimistic about how far and how fast they would be able to go over the last five years."

Long-delayed elections have now been put off until early next year, under a deal signed by President Michel Martelly.

Martelly has called for the parliament to convene on January 12 to endorse the appointment of new Prime Minister Evans Paul, who will be tasked with forming a government.