New York's top prosecutor on Monday asked a judge to order Donald Trump's son Eric to testify in a probe into the Trump Organization's financial dealings.

According to court documents, the Trump Organization – the Republican billionaire president's real estate group – for months has stonewalled the investigation into allegations the company falsified asset values on its financial statements.

New York's Attorney General Letitia James launched the inquiry in March 2019 after Michael Cohen, Trump's former personal lawyer and fixer, testified before Congress that the company had inflated assets when seeking loans, while deflating them to pay less in real estate tax.

According to James' office the Trump Organization has refused to comply with seven subpoenas linked to the investigation that would provide prosecutors with a trove of documents and witnesses.

Eric Trump, who works as the group's executive vice president, has refused to testify under oath "despite his being an important character in certain transactions," the attorney general's office said.

"For months, the Trump Organization has made baseless claims in an effort to shield evidence from a lawful investigation into its financial dealings," James said in a statement. 

"They have stalled, withheld documents, and instructed witnesses, including Eric Trump, to refuse to answer questions under oath."

The announcement comes on the day Trump opened his bid for a second term, accepting the Republican nomination at the party's convention.

His son Eric is set to speak at the event Tuesday.

Trump Organization-owned properties under investigation include 212 acres north of Manhattan, a mixed-use building in lower Manhattan, Chicago's Trump hotel and residential complex, and a golf club in Los Angeles.

It's one of several investigations into the Trumps. Last year New York federal district attorney Cyrus Vance launched a probe into Trump's payments in 2016 to allegedly buy the silence of two women who claimed to have had affairs with him.

Court documents have suggested that Vance's grand jury probe has now expanded to possible banking and insurance fraud.

Last week a federal judge refused the president's effort to block the release of his financial records by a New York grand jury, saying Trump's grounds amounted to a "back door" attempt to invoke absolute immunity after the president's lawyers' were denied by the US Supreme Court in July. Eric Trump, 36, and his brother Donald Jr took over the organization after their father's inauguration.