Pete Buttigieg, the liberal mayor of a small American city in the conservative bastion of Indiana, officially launched his presidential bid Sunday, joining a crowded field of Democrats vying for their party's nomination in 2020.

The 37-year-old Rhodes scholar and Afghanistan war veteran is the two-term mayor of his hometown of South Bend -- a left-leaning bubble in America's so-called "Rust Belt" region, where the decline of industries such as steel and automobile manufacturing has hurt local economies.

In the three months since he declared an exploratory committee to test a presidential run, Buttigieg has raised $7 million, more than most other candidates, and jumped to third place in the latest polls of voters in Iowa and New Hampshire -- the earliest states to vote in next year's primary elections.

The popular mayor who speaks eight languages and plays classical piano has been the focus of countless news stories and profiles.

The fascination has been in no small part due to his background: he would be the youngest, first openly gay, first millennial and first mayor to become president.

But Buttigieg must still overcome the perception that his youth and thin resume as mayor of a town of just 100,000 leaves him lacking the experience necessary for the presidency.

"I recognize the audacity of doing this as a Midwestern millennial mayor," Buttigieg said. "But the moment we live in compels us to act."

Drew Corbin, a 24-year-old college student clutching four campaign T-shirts he had purchased for friends and wearing a campaign cap, said he still had not fully committed to the candidate.

"There's a lot of candidates. I don't want to make up my mind so soon, almost a year before the primaries," Corbin said. "But he's definitely my favourite right now."

- 'Destined for national politics' -

Buttigieg's launch at Studebaker called to mind the plant's closure in 1963 that was still reverberating in the city in 2011 when he was elected mayor.

He set out to tear down decaying, abandoned homes and restore the blighted Studebaker complex to make it suitable for new high-tech companies.

In an unlikely feat, the city has reversed decades of population decline and attracted new businesses and development, with the mayor's popularity growing in the process.

"His appeal, for many people in South Bend, is his ability to look forward and to focus on better days ahead," South Bend-based political science professor Elizabeth Bennion of Indiana University told AFP.

"Once people looked at his resume and heard him speak, many started talking about the fact that he was destined for national politics."