HONG KONG (AFP) - Hong Kong pro-democracy lawmakers announced Friday (May 19) they will pursue a bid to impeach the city's outgoing leader after he intervened in a probe into his own acceptance of large undeclared payments from an Australian company.

Chief Executive Leung Chun Ying in 2014 denied allegations made by an Australian newspaper that he had failed to declare HK$50 million (S$8.9 million), which he received from Australian engineering company UGL while in office.

The payments relate to a deal struck in December 2011 - months before Leung took office, but a week after he announced his candidacy - during UGL's purchase of insolvent property services firm DTZ, for which Leung was director and chairman of its regional operations.

Pro-democracy lawmakers on Friday decided to pursue impeachment after it was found on Monday that a document submitted to a legislative committee looking into the issue contained changes that were traced back to the chief executive.

"We want the legislative council archives to record that as chief executive, Leung has done something as improper as this, and to defend the legislative council, which should not face interference from the chief executive," pro-democracy lawmaker Dennis Kwok told reporters Friday.

"There's still slightly over a month to go for Leung's term, but we feel this matter is very serious, so after some deliberation we decided we should still go ahead with the impeachment," lawmaker James To said, adding the impeachment motion is expected to be finalised on Monday.

Leung is set to be replaced by his deputy Carrie Lam on July 1.

The outgoing leader on Tuesday had admitted he made the changes but denied any wrongdoing, adding that he made suggestions to the "scope" of the investigation.

The city's graft-buster, the Independent Commission Against Corruption, has also been investigating the case for more than two years, but has not arrived at any conclusion.

In February, Hong Kong's former leader Donald Tsang was found guilty of misconduct during his time at the helm in a high-profile corruption trial that rocked the city. He was given a 20-month jail sentence but was granted bail in April.

In 2014, Tsang's deputy Rafael Hui was jailed for seven-and-a-half years after being found guilty of taking bribes from Hong Kong property tycoon Thomas Kwok.