US President Donald Trump and First Lady Melania Trump make their way across the South Lawn upon return to the White House on 12 November 2019 after spending the weekend in New York. (AFP)

US Democratic lawmakers on Tuesday unveiled a list of eight more witnesses who will testify in open hearings as part of the impeachment investigation into President Donald Trump.

Lawmakers have already heard from all eight in closed-door hearings over the course of the investigation, which Democrats, who control the House of Representatives, launched in September.

Trump faces possible removal from office over allegations that he abused his powers by pressuring Ukraine to supply damaging information on rival Democrats and possible 2020 presidential election challenger Joe Biden.

But thanks to the Republican majority in the US Senate, which would take a final vote on the matter, it is ultimately unlikely that Trump would be removed.

Next Tuesday, the House Intelligence Committee will hear from Jennifer Williams, an aide to Vice President Mike Pence, and Alexander Vindman, an army lieutenant colonel and member of the National Security Council, according to a statement from the committee.

Later that afternoon, Kurt Volker, who was US special envoy to Ukraine until September, and White House Russia specialist Tim Morrison, will testify.

American ambassador to the European Union and Gordon Sondland, who has already delivered one of the most damning testimonies of the affair, will testify again next Wednesday.

He admitted earlier this month that he had linked US military aid to Ukraine with the country opening an investigation into Biden.

On Wednesday afternoon, Laura Cooper, the Deputy Assistant Secretary of Defense for Russian, Ukrainian, and Eurasian Affairs, and David Hale, the Under Secretary of State for Political Affairs, will appear before the committee.

Then Fiona Hill, the former National Security Council director for Europe and Russia, will appear Thursday morning.

And according to the statement, Democrats have “accepted all of the (Republican) requests that are within the scope of the impeachment inquiry,” though it did not offer more details.

Public hearings are set to start Wednesday morning with William Taylor, the top US diplomat in Ukraine, and George Kent, Deputy Assistant Secretary of State for European and Eurasian Affairs.

Former US ambassador to Ukraine Marie Yovanovitch is expected to appear Friday.