International donors pledged $6 billion in aid for war-ravaged Syria on Wednesday as the UN Security Council held emergency talks over a suspected chemical attack that killed dozens in a rebel-held town.

Donors from more than 70 countries meeting at a conference on Syria in Brussels made a "collective pledge of $6 billion for this year alone", EU Humanitarian Aid Commissioner Christos Stylianides said.

Stylianides described the pledge which appeared to approach the conference hosts' target as "an impressive figure".

Syria's "needs are massive. Our conference is sending a powerful message," he said.

Nearly half the Syrian population has been displaced by the violence, with millions seeking sanctuary in neighboring Lebanon, Jordan and Turkey, or heading further west to European countries.

UN agencies estimate war damage across Syria so far at $350 billion, including physical destruction and the loss of economic activity. Four out of five people are living in poverty.