What are effective ways to handle meltdowns in class?

I work with students who struggle with emotional regulation... I’m looking for effective ways to help them when they experience these meltdowns in the classroom. I want to make sure I’m responding in a way that really helps them (it's hard to tell sometimes) rather than escalating the situation.

I basically just try to use calm and reassuring language, but at times it really feels like nothing works and the students just shut down completely.. or worse, become disruptive / aggressive. I’d love to hear what works for others. Thank you!