The Associated Press and other US media outlets say Vice President Kamala Harris has secured the support of enough Democratic delegates to be nominated as the party's presidential candidate.

Harris said in a statement on Monday that, "I look forward to formally accepting the nomination soon."

A growing number of delegates has been pledging support for Harris amid a lack of candidates for the nomination race.

About 4,000 delegates are to vote to choose the party's presidential candidate. The Associated Press said its survey shows Harris has secured the backing of at least 2,668, significantly more than the 1,976 votes she needs for the nomination.

The Democratic National Committee said on Monday it will determine the party's presidential nominee by August 7 through online voting, ahead of the national convention that opens on August 19.