Lithuania has built the first stretches of a steel border wall since migrants from the Middle East and other areas began entering from Belarus this year.
The European Union accuses Belarus of deliberately encouraging the migrants to enter EU states Poland, Lithuania and Latvia via Belarusian territory as a way of putting pressure on the bloc.
Belarus has repeatedly denied this but its president, Alexander Lukashenko, has said his country would no longer stop the migrants, since EU sanctions drain resources.
All three EU countries have put stretches of razor wire on the border to stop the migrants. Last week Lithuania began putting up the first stretches of the 3.4-metre (11-foot) high steel fence, topped with 0.6 metres (2 feet) of razor wire.
Planned walls around Belarus
"It’s probably impossible to build a totally unpassable obstacle, so I think that this barrier can too be overcome. But that would take a long time, and we would be able to react", said Virgilijus Raugale, the chief boarder guard in southern Lithuania.
Lithuania has allocated 152 million euros (£130m) to build 500 kilometres (300 miles) of the wall by September next year. The wall is supplemented by a 3-metre high heap of coiled razor wire next to it and video surveillance equipment.
More than 4,000 migrants entered Lithuania from Belarus this year before August, when the country resorted to sending almost all entering migrants back to Belarus.
Over 5,600 migrants were prevented from entering since then, the border guard service said, including 2,300 who tried to enter in October.
Workers install a four-metre-high fence on the Belarusian border in Druskininkai, Lithuania
Meanwhile, Poland said on Friday a Belarusian soldier tried to fire flares at Polish border troops and others tried to tear down fencing along the frontier amid rising tension over a wave of migrants trying to reach EU territory from Belarus.
"Further provocations at the border. Yesterday, a Belarusian soldier tried to fire a flare gun towards Polish soldiers. Fortunately, the gun did not fire," the Polish defence ministry wrote on Twitter.
"100 metres away, five armed Belarusians tried to destroy (our border) fence, shouting at the same time that they would shoot Polish soldiers."
Poland has erected a barbed-wire fence along the border, where a state of emergency is in effect, to keep out arriving migrants and plans to build a 5.5-metre (18-foot)-high wall along a 180-km (110-mile) stretch of the boundary.
Other fences in th EU
Anton Bychkovsky, spokesperson for the Belarusian State Border Guard Committee, told the Sputnik Belarus news agency that the Polish side was inventing facts.
"The adjoining side continues to escalate the situation around the situation on the border. Representatives of the Polish Ministry of Defence are in fact provocateurs themselves," Sputnik quoted him as saying.
The Belarusian foreign ministry did not immediately respond to a request for comment.