Budapest plans to send soldiers to help police at the border where thousands of migrants arrive from Serbia every day.
A new razor-wire barrier is already being built along the frontier. MPs are expected to vote on stricter border controls later this month.
Authorities have been told to expect 40,000 more migrants by next week.
Many of them are fleeing conflicts in countries like Syria and Libya and are trying to travel through Hungary to Germany, Austria and Sweden – wealthier EU nations with more liberal asylum laws.