The award-winning young adult author Patrick Ness’s fundraiser for Syrian refugees topped half a million pounds this morning, after writers including Philip Pullman, Marian Keyes and Anthony Horowitz joined the cause over the weekend.

Ness, who won the Carnegie medal twice in 2011 and 2012, began fundraising for Save the Children on the morning of 3 September, saying he was “tired of just tweeting my despair about the current refugee crisis that the UK government is responding to with inhumane feebleness”. He promised to match funds raised by the public up to £10,000 – a target that was reached in under two hours, with fellow authors John Green, Derek Landy and Jojo Moyes each then pledging to donate £10,000 of their own, matching public donations.

The total raised stood at £452,700 this morning, or £517,600 with gift aid added, with dozens of writers and publishers having contributed donations, including Jessie Burton, Jill Mansell, and most recently Pullman, who promised to donate £10,000 when the total reached £435,000. “C’mon, give him a reason to get book four out,” tweeted Ness, referring to Pullman’s long-awaited follow-up to the acclaimed His Dark Materials trilogy, The Book of Dust.

We crossed £425k, which means @PhilipPullman is on the clock! Cross £435k & he donates £10k. C'mon, give him a reason to get book four out! — Patrick Ness (@Patrick_Ness) September 6, 2015

“I just can’t believe what we – not me, we – have achieved in just four days,” Ness told the Guardian this morning. “Over £500,000, way more than I ever could have dreamed in an angry moment on a Thursday morning. The support from authors has been incredible and keeps coming! Just amazing, what a wonderful community.”

On Twitter, he thanked publishers Andersen Press, Walker Books and Candlewick, “who donated very large amounts for not being the biggest publishers *cough*”, as well as publisher Scott Pack, who auctioned a full editorial review of a manuscript, raising £1,300, authors from the Children’s Writers and Illustrators Group conference, who pledged £3,000. Ness has also donated an additional £5,000 himself, after the fundraiser drew 5,000 donors.