Poor love. Beginnings are tough at the best of times.
And
that they aren't supporting you, or him - although I know 30 new kids is a lot to manage, and sometimes it takes a week or two for teachers to figure out who needs what at the start of a new year.
I would imagine some of the tears are about missing the old - ie nursery - as much as 'not liking the new'. dd1 has always, but always, shed tears at the start of a new academic year as she misses the safety and familiarity of the past. She used to express it as 'I hate the new teacher/class/whatever' but now in Y3 is learning that its really more that she misses the old one.
BUT if my child was genuinely terrified, I would expect the school to work with me - ask them for suggestions, make an appointment to talk to the teacher after school when she has time. Is there a TA who can spend a few minutes with him when you leave in the morning? Is there an adult he can begin to trust tomorrow?
I would also explain there is no option but to go (firm and gentle) and ask him what he thinks might help - can he take in a favourite cuddly/toy to put in a safe place and bring out if he feels sad? Does he need a tiny pebble, a note, soemething from you in his pocket, to remind him he's loved and safe and will be going home later?
Sympathies - its really hard when they're upset like this. Good luck tomorrow, hope the week improves...