WASHINGTON - Presidential contender Bernie Sanders raised $18.2 million in the first three months of the year for his 2020 White House bid, his campaign said on Tuesday, giving him an early fundraising lead in a crowded Democratic primary field.

Sanders, a U.S. senator from Vermont making his second run for the White House, received 900,000 donations from 525,000 individual donors with the vast majority under age 39, campaign manager Faiz Shakir told reporters. The average donation was $20.

About 20 percent of donors were new supporters of Sanders, he said. Sanders ran for the presidency in 2016, but lost the Democratic nomination to Hillary Clinton.

Fundraising totals are a closely watched early indicator of a candidate's support, and Sanders has outpaced the other two Democrats who have announced totals. U.S. Senator Kamala Harris of California raised $12 million, and Pete Buttigieg, the mayor of South Bend, Indiana, said he raised $7 million in the first quarter.

The field of Democrats vying for the right to challenge Republican President Donald Trump includes other candidates with proven fundraising ability, including Beto O'Rourke, the former Texas congressman who said he raised $6.1 million in a day after he entered the race last month.

Candidates are required by law to track and report all campaign donations, and those collected in the first quarter must be disclosed by April 15. Candidates are limited to collecting $2,800 from a single donor during the primary process.

Sanders campaign officials said his first-quarter haul, which included donations from all 50 states, will allow him to expand campaign staff and operations in early voting states in next year's primary contests, which kicks off in Iowa in February.

"With the money we have raised, we will be able to compete in all of the states" through early March 2020, said Jeff Weaver, a senior adviser to Sanders.