My now 4 year old definately had some extremely intense tantrums in his twos & threes. He always had a difficult time calming down once he got upset, even as an infant. This is what we found helpful--we tried to stay really aware of his triggers (although sometimes they were a complete surprise). Things like transitions, too many "no"s in a day, too many people, stores, etc. could all add upto a meltdown. On days when those things were going to happen (a day of errands for example), i'd try to build in lots of space for the things that recharged him--playground breaks between stores, etc. We also built in lots of awareness of transitions--telling him in advance what we were doing, then reminding again & again. There were times we left all the purchases & walked out of the store because I could see that we were headed into a tantrum. There were also times when I sat down on the ground next to him, said loving things & waited it out in the middle of the store, park...
I would do my best to identify triggers, looking beyond the immediate trigger to the whole day--sleep, food, activites, etc. When the tantrum happens, as long as your both safe, sit next to him (I like the objective, compassionate observations a previous poster mentioned), talk to him gently. I also recommend "Raising your spirited child" by Mary Sheedy Kuchina.
Know that this will pass--My son does still have melt-downs, but the intensity is markedly less & much more easliy identifiable. I also know what he needs in a day to keep himself resiliant (for him, lots of outside time, some mama snuggles, certain amount of time to himself with self-directed play, stories, time in the water). Good luck!