Sen. Bernie Sanders's (I-Vt.) presidential campaign raised $18.2 million in the first quarter of 2019, his advisers said Tuesday, a massive sum that is likely to put the progressive firebrand among the top fundraisers of the early 2020 Democratic primary season.

Sanders, who announced his second bid for the White House in February, has already proven to be an adept fundraiser, raising nearly $6 million in the first 24 hours after launching his campaign. By the end of his first week on the trail, he had raised $10 million.

Sanders's campaign manager, Faiz Shakir, said the senator's first-quarter fundraising total was powered by roughly 900,000 individual donations with an average contribution size of $20, a number that Sanders is likely to highlight given an increasing focus on grass-roots giving in Democratic politics.

Shakir said 525,000 individuals across all U.S. states and territories gave to the campaign. The average age for Sanders's donors was under 39 years old, he said.

"Supporters have shown up big time for this campaign. Huge, you could say," Shakir told reports.

The fundraising numbers put Sanders's total haul for the quarter at $32 million, including $14 million that the senator had in other accounts to start with. Shakir said that the campaign finished the first quarter of 2019 with $28 million in cash on hand.

The fundraising total announced by Sanders's campaign Tuesday surpasses the amount he raised in the first months of his 2016 presidential bid. That year, he reported bringing in $15.2 million from April 30, the day he launched his campaign, to June 30.

The first-quarter haul sets up Sanders's campaign to expand its operations in key early-voting states, said Jeff Weaver, a senior adviser to Sanders. He said that the campaign would add more staffers to its operation in Iowa and would begin staffing up in California in the coming weeks, as well.

"These resources are going to allow us to compete on all levels in all of the Super Tuesday states," Weaver said in a conference call, referring to the day in 2020 when eight states hold primary contest.

"While we had to in 2016 make choices about where we could compete ... this campaign will have the resources and the volunteer grass-roots strength to compete in every state in the primary process."

During his first presidential bid in 2016, Sanders made corporate influence in politics a key issue, touting his refusal to take money from corporate political action committees (PACs).

Virtually every Democrat in the 2020 race has similarly sworn off corporate PAC money - and, in some cases, PAC money in general - and has emphasized the role of small-dollar donations in their fundraising efforts.

The campaign finance filings cover the period from Jan. 1 to March 31. Candidates have until April 15 to submit their fundraising reports to the Federal Election Commission.

Some candidates have already announced their first-quarter totals.

Sanders became the third 2020 Democratic presidential hopeful to announce his or her first quarter fundraising haul. South Bend, Ind., Mayor Pete Buttigieg said Monday that his campaign had raised $7 million in the first quarter, while Sen. Kamala Harris (D-Calif.) said she raised $12 million.

Another proven fundraiser, former Rep. Beto O'Rourke (D-Texas), has yet to post his first-quarter total. That number is expected to rival Sanders's. In the first 24 hours of his presidential campaign, O'Rourke said he had raised some $6.1 million.

Updated at 10:50 a.m.