Donald Trump, once a cryptocurrency skeptic, vowed Saturday to be a "pro-bitcoin president" if elected in November, as the Republican nominee sought backing from an industry irked by US regulations.

"The Biden-Harris administration's repression of crypto and bitcoin is wrong, and it's very bad for our country," Trump said to cheers at a conference in Tennessee.

The ex-president likened cryptocurrencies to the growth of the "steel industry of 100 years ago", and said "Bitcoin stands for freedom, sovereignty and independence from government coercion and control."

Trump said if he was in the White House, he would not allow the US government to sell its bitcoin holdings.

"This will serve in effect as the core of the strategic national bitcoin stockpile," Trump said.

The proposal was more limited than one offered the day before by longshot third-party candidate Robert F. Kennedy Jr., who said he would seek to build a stockpile of 4 million bitcoins.

"If we don't embrace crypto and bitcoin technology, China will, other countries will, they'll dominate, and we cannot let China dominate," Trump said Saturday.

"If crypto is going to define the future, I want it to be mined, minted and made in the USA."

Acknowledging the price of electricity as a key factor in where cryptocurrency mining operations are located, Trump vowed to make US energy the cheapest "of any nation on Earth" by increasing fossil fuel production and through nuclear energy.

"We'll be doing it in an environmentally friendly way, but we will be creating so much electricity that you'll be saying, 'please, please, Mr. President, we don't want any more electricity.'"

He said on his first day in office, he would fire Gary Gensler, the chairman of the US Securities and Exchange Commission (SEC), a frequent target of cryptocurrency industry outrage over his cautiously slow approach to implementing regulations.

The crowd roared with approval at the proposal, prompting Trump to joke: "I didn't know he was that unpopular."

"Let me say it again. On day one, I will fire Gary Gensler!" he said, with the crowd erupting again.

He also targeted Vice President Kamala Harris, who is set to replace Biden atop the Democratic ticket following the 81-year-old president's shock exit from the campaign.

"We have to fight and we have to win, and I pledge to the bitcoin community that the day I take the oath of office, Joe Biden, Kamala Harris's anti-crypto crusade will be over, it will end, it'll be done," Trump told the crowd.

"You're going to be very happy with me."