Hungary will build a new, 'more massive' fence on its southern borders to defend against a possible surge in the number of migrants, Prime Minister Viktor Orban said on Friday.

Orban, who earlier said migrants were 'poison', said on state radio that there may soon be a 'greater need for security' and the fortified barrier would be able to stop 'several hundreds of thousands of people' at the same time, if needed. He did not say when construction could start.

Orban said the surge could take place if, for example, Turkey allows the millions of refugees living there to leave for Western Europe.

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Children play at a makeshift camp for migrants in Horgos, Serbia, meters away from Serbia's border with Hungary

'Then, if we can't do it nicely, we have to hold them back by force,' Orban said. 'And we will do it, too.'

Hungary built fences protected with razor wire on its southern borders with Serbia and Croatia last year, when nearly 400,000 people passed through the country on their way west.

The fences have greatly slowed the flow of people entering Hungary, which is also beefing up its police force with 3,000 new 'border hunters' to tighten control at the fences.

It has also introduced controversial legislation that allows officials to return migrants to Serbia if they are caught within eight kilometers (five miles) of the border.

A migrant child eats in Horgos. Hungary built fences protected with razor wire on its southern borders with Serbia and Croatia last year, when nearly 400,000 people passed through the country on their way west

Children carry water at the Horgos camp. Orban reiterated his call for the stronger protection of Europe's external borders

Hungary has denied repeated allegations that officers have used force to 'escort' the migrants and refugees back to Serbia.

Orban reiterated his call for the stronger protection of Europe's external borders, saying joint efforts were needed to defend the borders between Serbia and Macedonia and Macedonia and Greece.

'Immigration and migrants damage Europe's security, are a threat to people and bring terrorism upon us,' Orban said, adding that this was caused by allowing the uncontrolled entry of large numbers of people 'from areas where Europe and the western world are seen as the enemy.'

Orban's virulent anti-migrant stance also includes a government-sponsored referendum on October 2 seeking political support for the rejection of any European Union plans to resettle migrants among its member countries.