Marcus's guess was correct; this was indeed a portal break, and it was a particularly rampant one as well. A large number of beasts had stormed the city, and it had happened all too fast.
Warriors of the Lost Clan were fighting at the entrance against the beasts, as the portal hadn't opened within the city itself. The beasts, strange creatures with large heads, had overwhelmed the city.
They were strong, powerful, fast, and their saliva seemed to have a melting property in it, allowing them to stop most weapons. If weapons were coated in strong Qi, they could resist the saliva, but this wasn't something that could be done against many.
With the beasts having entered the city, they were reacting to any signs of life, taking them out. Another thing to note of the beasts themselves, it was almost as if they had no eyes.