"My best guess is that by the end of the day we will have heard pledges for 2018 of $4.4 billion," Mark Lowcock, the head of UN aid agency UNOCHA, told a news conference.
"I want particularly to thank the EU, Germany and the United Kingdom who have made exceptionally large pledges today," Lowcock said.
Pledges of a further $3.3 billion for 2019 and after were expected at the conference, which groups more than 80 countries, aid groups and agencies, he added.
The money is needed for humanitarian work inside Syria and to support refugees in neighbouring countries, the UN says.
The UN official had earlier told AFP he hoped to see $8 billion pledged on Wednesday, warning that some programmes may need to be cut if funds are not forthcoming.
London and Berlin led the pledges on Wednesday, with Britain announcing 450 million pounds ($630 million, 515 million euros) for 2018 and another 300 million pounds for 2019, while Germany said it would donate more than a billion euros.
Some 6.1 million people are now internally displaced in Syria, more than five million have fled the country and 13 million including six million children are in need of aid, according to the UN.
More than 700,000 people have been displaced since the start of this year alone as Assad has stepped up his offensive against rebel forces, intensifying the humanitarian crisis.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.