Help!What do I do when my cat is chocking on string?

Okay,so yesterday my mom left string things laying on her bed,and while we were gone for the day he ate the string.He is now trying to regurgitate it.He has been vomiting all day,and each time I see the string hanging out of his mouth he swallows it before I can see if it's loose enough to pull out.Please help!The vet is closed today and tomorrow!