The Liberal Democrats claim to have raised more than twice as much as Labour from individual donors since a snap election was called.
All parties have made cash appeals to supporters after Theresa May's surprise decision to hold an election on 8 June.
The Lib Dems say they raised £500,000 in 48 hours.
A similar Labour fund-raising drive is reported to have raised £200,000. Labour has yet to comment on the figure, reported by the FT.
The Conservatives have been contacted for details of their fundraising efforts.
Lib Dem leader Tim Farron claimed activists and donors were "flocking" to his party on the back of its anti-Brexit message.
The party, who are arguing for another referendum on the final Brexit deal, say they have seen their membership jump to 95,000, attracting 8,000 new members since Tuesday alone.
The Lib Dems also raised £1.972m in donations in the final quarter of 2016 - more than Labour over the period.
Labour saw a massive increase in membership - to more than 500,000 - after Jeremy Corbyn's election in 2015, although a report leaked to The Guardian suggested 26,000 had left since last summer.
Speaking in Swindon on Friday, Mr Corbyn said Labour had signed up a further 2,500 members since the election was called.
The Lib Dems have traditionally struggled to match the Conservatives or Labour in terms of big donations and tend to spend far less on advertising at general elections than the two bigger parties.
They launched an emergency fund-raising drive on Wednesday after Parliament approved Mrs May's surprise decision to seek a snap general election.
The party is attempting to recover from their 2015 electoral wipe out, which saw them lose nearly 50 Commons seats.
Opinion polls suggest they are unlikely to get the 57 seats they won in 2010, let alone the 62 seats they won in 2005 when Charles Kennedy was leader.
Lib Dem strategists point to their success in November's Richmond Park by-election, where Sarah Olney overturned a 23,000 Tory majority, as proof they can win back constituencies which voted overwhelmingly to remain in the EU.
But critics say they could be vulnerable in existing and target seats which voted Leave in the EU referendum.
Mr Farron has said only his party stood in the way of the Conservatives substantially increasing their majority.
Some senior Lib Dems, including former leader Lord Ashdown, have backed co-operation with other "progressive" parties to keep Conservatives from winning certain seats, while the Greens have backed local electoral pacts in some seats.
But the Conservatives have accused the Lib Dems of being determined to defy the will of the people and overturn Brexit.
They have also warned of a "coalition of chaos" with Labour and the SNP, prompting the Lib Dems to distance themselves from talk of working with Labour in the event of a hung Parliament.