US President Barack Obama (L) joins former President Bill Clinton onstage after Clinton nominated Obama for re-election during the second session of the Democratic National Convention in Charlotte, North Carolina, September 5, 2012. [Photo/Agencies]

CHARLOTTE, the United States - US Democrats officially nominated President Barack Obama as its presidential candidate for the November 6 election during a roll call vote running through late Wednesday night to early Thursday, following former President Bill Clinton's nominating address.

Obama has passed the threshold of required 2,777 delegates halfway through the roll call vote of delegates from 50 states, the District of Columbia and US territories, during the second day of its national convention in Charlotte, North Carolina.

Obama will formally accept the party's nomination on Thursday night and deliver his prime time speech.

The focus of his acceptance speech will be a "forward-going" plan, said the Obama campaign.