Former US Vice President Joe Biden maintained his national lead in the polls after December's sixth Democratic Party presidential debate, said a poll statement.

The latest data by the Morning Consult, a daily polling survey, showed that Biden led the poll with 31 per cent support for the second week in a row, two points higher than the first week of the month, Xinhua news agency reported.

Bernie Sanders, US senator of the state of Vermont, followed Biden with 21 per cent support.

Senator Elizabeth Warren and Pete Buttigieg, mayor of South Bend in the state of Indiana, kept the third and fourth place with 15 percent and 9 percent, respectively.

The 2020 Democratic Party presidential debate takes place among candidates in the campaign for the party's nomination for the US President in the 2020 presidential election. The next debate is scheduled for January 14, 2020.ians