Pete Buttigieg is no longer the mayor of South Bend, Indiana, but his presidential campaign is going from strength to strength in terms of raising cash.

The 37-year-old raised $24.7m in the fourth quarter, his campaign announced on Wednesday, up on the $19.1m he collected in the previous fundraising period.

Buttigieg has come under fire over his successful fundraising efforts. On the debate stage in December the Massachusetts senator Elizabeth Warren attacked the mayor regarding fundraisers including a now infamous occasion in a Napa Valley wine cave.

Buttigieg’s time as mayor of a small city in northern Indiana ended on New Years’ Day, leaving him free to concentrate on a Democratic primary in which he has surged from unknown to top-tier contender.

He leads polling averages in Iowa, the first state to vote, and is second in New Hampshire, the next target in the race for the nomination to face Donald Trump in November.

However, the realclearpolitics.com national polling average for the Democratic field, which is still an unwieldy 15 candidates strong, puts Buttigieg 20 points behind the frontrunner, former vice-president Joe Biden.

The Vermont senator Bernie Sanders, second nationally, 10 points adrift of Biden, had the largest fundraising haul in the third quarter, raising $25.2m.

Warren – third nationally, seven points up on Buttigieg – has both said she will not hold any fundraisers and accused the mayor of being influenced by big donors.

“When a candidate brags about how beholden he feels to a group of wealthy investors,” she said in a December speech, “our democracy is in serious trouble”.

Sanders has also attacked. Last month, the senator told the Guardian that the support Buttigieg was receiving from billionaires was “exactly the problem with American politics”.

Buttigieg has opened fundraisers to the press and disclosed the identities of top donors. But he has also insisted Democrats need to fundraise from anyone, so they can remain competitive against Trump, who has amassed a formidable war chest.

On Tuesday, Buttigieg closed out 2019 with a series of appeals for donations. On Twitter, he said: “We’ve taken our message about the purpose of the presidency and the possibilities for our politics from obscurity to the top tier of our country’s political process.

“We have a lot of work ahead of us. But unlike a year ago, we’ll do it with strong, national grassroots support.”