WASHINGTON, USA (AFP) — Republican Mitt Romney raised more than $170 million in September, aides said yesterday -- a record for his campaign, but shy of President Barack Obama's $181 million haul for the same period.

With the latest fund-raising figures, the Romney campaign and the Republican National Committee (RNC) plus state party participants now have more than $191 million cash on hand, just 22 days before the general election.

Romney and running mate Paul Ryan "are offering voters a vision for our country that will grow the economy, increase incomes and bring relief to the middle class," Romney Finance Chairman Spencer Zwick said in a statement.

"That is why we are seeing such strong support from donors across the country."

The campaign said Romney and the RNC registered donations of under $250 from more than 1.01 million people for the month, with 93.1 per cent of donations at $250 or less.

That compares with 1.8 million Americans donating under $250 to Obama and the Democrats, with 98 per cent of all Democrat contributions at $250 or less, according to figures released by the Obama campaign on October 6.

Romney's substantial haul means that he, like the incumbent, will have big money to lay out on an advertising blitz in the final three weeks before the November 6 election.

But Obama's 1.8-million donors for the same month compared with one million for Romney, suggests broader grass roots support for the president.

It is the second month in a row that Obama has outraised his Republican challenger, following three straight months of Romney posting bigger numbers.

Romney spent much of his time in September hitting up wealthy donors, attending at least 23 private fund-raisers during the month, according to a Washington Post count. He earned criticism from some observers who questioned whether he was spending enough time on the campaign trail.

Obama attended at least 13 fund-raisers during the same period.