Janos Lazar, Prime Minister Viktor Orban's chief of staff, also said once new rules are in place, any migrants detained anywhere in Hungary without documents allowing them to be in the country will be returned across the border.

Human rights advocates noted that Hungary was already holding large numbers of asylum seekers in closed camps and that the massive, indiscriminate detention of all asylum seekers "has not been seen in decades in democratic Europe".

The Hungarian Helsinki Committee also vowed to sue Hungary at the European Court of Justice in every case where asylum seekers are illegally kept in custody, which would be likely to force the country to make compensation payments.

"The government would do better instead to improve the quality of the open reception centres and spend this money on the integration of people who have found asylum in Hungary," the group said.

Presently, asylum seekers whose claims are under appeal are placed mostly in open camps and some leave for western Europe before their cases are decided.

Migrants detained within eight kilometres of the border are sent back across the fences Hungary has built on its southern borders with Serbia and Croatia.

Mr Lazar said the measures will be enacted only when, like at the present time, the government declares a state of emergency because of mass immigration.

"It is clear that the security situation in Europe has deteriorated, not improved," Mr Lazar told reporters after a government meeting.

"Turkey is presently defending the borders of Europe. We would like to strengthen the Hungarian border."

Mr Lazar reiterated that Hungary was ready to build a second, stronger fence if needed, on its southern borders, and is building several small bases along the fence for the thousands of border police.

Mr Lazar also said the government would increase aid to charity groups working along the border.

Hungary granted asylum or some form of protection to 425 people in 2016, while receiving 29,432 applications.