Hungary declared a state of emergency and said troops would be deployed to reinforce its borders following the closure of a key migration route.
European leaders' move this week to close the Western Balkans route and consider Turkey's offer to take back any migrants or refugees drew condemnation and outrage from human-rights groups.
Closing the route has left around 14,000 desperate people stranded along the Greek border with Macedonia amid rapidly-deteriorating conditions.
Dozens more were arriving under heavy rains Wednesday at the overflowing refugee camp in the Greek town of Idomeni despite the border closure, according to The Associated Press. Human-rights workers said the border was completely closed.
Hungary's Interior Ministry said the state of emergency over "mass migration" was declared because "we do not know what reaction" tightened border restrictions in neighboring nations "could trigger among refugees" and migrants.
Slovenia, Croatia and Serbia put new measures in place requiring EU visas at their borders in an attempt to limit the number of migrants crossing — effectively cutting off the well-traveled Balkans route.
Hungary's Interior Ministor Sándor Pintér said there are an estimated 10,000 people in those countries without "valid" permits.
"We do not know what direction they will begin moving in, and therefore if needed we must prepare to defend our borders effectively," he said in a statement.
Borders will be strengthened and some 1,500 members of the Hungarian Defense Force along with "large numbers of police" will be involved, according to the Interior Ministry.
Violent scenes broke out in Hungary last year when the migrant crisis hit full swing, evoking outrage and allegations of heavy-handed police tactics toward new arrivals.
Pinter said Wednesday that centers for asylum requests are currently full which could "cause turmoil similar to last year."
Resources will be deployed to ensure the "entire border" can be illuminated at night along the newly-constructed border fence to help catch anyone attempting an illegal crossing, Pinter added.
Hungary's move was the latest in a line of actions aimed at restricting movement on the Balkans route in direct response to Monday's European Union summit.
On Wednesday, the president of the European Council thanked Western Balkan nations for their efforts.