Former US president Donald Trump has appealed against a judge’s decision requiring him to answer questions under oath in New York state’s civil investigation into his business practices — a widely expected move that is likely to prolong the fight over his testimony by months.

Lawyers for Mr Trump and his two eldest children filed papers on Monday with the state’s trial court, seeking to overturn Manhattan Judge Arthur Engoron’s February 17 ruling.

They argue ordering the Trumps to testify violates their constitutional rights because their answers could be used in a parallel criminal investigation.

In an eight-page ruling, Mr Engoron set a March 10 deadline for Trump and his children, Ivanka and Donald Trump Jr, to sit for depositions.

Lawyers for the Trumps asked the appellate court for a stay to spare them from questioning while it considers the matter.

The court did not set a date for arguments. It typically issues decisions several months after that, but could be inclined to rule on an expedited basis given the urgency of New York Attorney General Letitia James’ investigation and the Trumps’ desire to swiftly overturn Engoron’s ruling.

A message seeking comment was left with James’ office. In a statement on Friday, as lawyers for the Trumps were preparing their appeal, the attorney general signalled she was ready for a long fight to get them to testify.

“Donald J. Trump, Donald Trump, Jr, and Ivanka Trump were ordered by the court to comply with our lawful investigation into Mr Trump and the Trump Organization’s financial dealings,” Ms James said in the statement.

“While they have the right to seek a delay, they cannot deter us from following the facts and the law wherever they may lead.

“Make no mistake: My office will continue to pursue this case without fear or favour because no one is above the law.”

Mr Trump did not immediately comment on the appeal. In a statement following Mr Engoron’s decision, he called the ruling “a continuation of the greatest Witch Hunt in history”.

He claimed he is unable to get a fair hearing in New York “because of the hatred of me by Judges and the judiciary” and accusing Ms James’ office of “doing everything within their corrupt discretion to interfere with my business relationships, and with the political process”.

Ms James, a Democrat, has said her investigation has uncovered evidence Mr Trump’s company, the Trump Organization, used “fraudulent or misleading” valuations of assets like golf courses and skyscrapers to get loans and tax benefits.

If Mr Engoron’s decision is upheld it could force Mr Trump into a tough decision about whether to answer questions, or stay silent, citing his Fifth Amendment right against self-incrimination.

Anything Mr Trump says in a civil deposition could be used against him in the criminal probe being overseen by the Manhattan district attorney’s office.

At a hearing prior to Mr Engoron’s decision, Mr Trump’s lawyers argued that having him sit for a civil deposition is an improper attempt to get around a state law barring prosecutors from calling someone to testify before a criminal grand jury without giving them immunity.

– AAP