A generation of Syrian children is facing "catastrophic" psychological damage, with 1 in 4 inside Syria at risk of developing a mental health disorder from witnessing traumatic events, a global children's charity said on Tuesday.

The psychological needs of children fleeing four and a half years of war remain largely unmet due to lack of funding, spiraling numbers of refugees and overstretched resources in host countries, Save the Children said in a report.

"The repercussions for the future mental health of an entire generation could be catastrophic," Ian Rodgers, country director for Save the Children in Lebanon, said in a statement.