US authorities charged a former president of the United Nations General Assembly, a billionaire Macao real estate developer and four others on Tuesday for engaging in a wide-ranging corruption scheme.

John Ashe, a former UN ambassador from Antigua and Barbuda who was general assembly president from 2013 to 2014, was accused in a complaint filed in federal court in New York of taking more than $1.3 million in bribes from businessmen, including developer Ng Lap Seng.

Manhattan US Attorney Preet Bharara, who announced the arrests of Ashe and the other defendants, said the investigation could result in more charges as authorities examine whether "corruption is business as usual at the United Nations".

"If proven, today's charges will confirm that the cancer of corruption that plagues too many local and state governments infects the United Nations as well," Bharara said.

UN Secretary-General Ban Ki-moon is "shocked and deeply troubled" by the allegations, said his spokesman, Stephane Dujarric. The UN had not previously been informed of the probe, Dujarric said, but would cooperate if contacted.

The case followed the Sept 19 arrest of Ng, 68, and an assistant, Jeff Yin, 29, for falsely claiming that $4.5 million they brought into the United States from 2013 to 2015 was meant for gambling or buying art, antiques or real estate.

Both men are charged in the latest case.

Bharara said authorities continue to examine funds connected to Ng, who prosecutors say has a $1.8 billion fortune, much of which he earned on developments in Macao.

According to the complaint, Ng, through intermediaries, paid Ashe more than $500,000 to submit a document telling the UN secretary-general that a yet-to-be built multibillion-dollar UN-sponsored conference center in Macao was needed.

The intermediaries included Francis Lorenzo, 48, a deputy United Nations ambassador from the Dominican Republic who prosecutors said Ng paid $20,000 every month as "honorary president" of one of his organizations, South-South News.