The best thing when you argue with someone is to apologize, like you did.
It happens to everyone to overreact sometimes and thus you should not feel anxious about it. Since you two know each other very well, he might understand that you did not mean the words you said and finally forgive you.
For now he is in control, and if he blocked you it's either to give you a lesson or because he wanted calm himself first before talking to you.
The best thing now is to wait for him to digest the argument and accept your apologies. Depending on how far your crossed the line and who your friend is, it might take some time.
I know it can be very frustrating to be unable to talk to someone and explain yourself, but try to tell yourself it is part of your apologies to give him a little bit of space.
I've already been in the exact same situation as you and the only time I could not fix my friendship is because I lost my calm due to the frustration of being blocked too long. So you get it, my advice is the same as your surrounding : now that you apologized, patience is key, and do not forget that the unblock button is as easy to press as the block button.
If you still don't have any news after a week, then you could try to reach one of his friends.