The Hungarian government says it expects up to 300,000 migrants to reach the country this year, around twice its earlier estimate.

Nearly 90,000 migrants have come to Hungary so far in 2015. Most continue to other parts of the European Union.

Janos Lazar, head of the Prime Minister's Office, said Tuesday that "Hungary has become one of the countries most exposed to illegal migration." He said the fence the country plans to build on the southern border with Serbia to stem the flow of migrants "needs to be built in the shortest term possible."

Lazar said most of the 175-kilometer (109-mile) Hungary-Serbia border would be protected by a chain-link fence dug 1.5 meters (5 feet) into the ground and rising 3 meters (10 feet) above ground, topped with razor wire.