Donald Trump cannot block a prosecutor's subpoena for eight years of his tax returns, a federal judge ruled on Thursday, in the latest setback in the US president's longstanding effort to keep his finances under wraps.

US District judge Victor Marrero in Manhattan rejected Trump's claims that the grand jury subpoena from Manhattan District Attorney Cyrus Vance to the president's accounting firm Mazars USA was "wildly overbroad" and issued in bad faith.