BREZICE, Slovenia — Led by riot police on horseback, thousands of weary migrants marched across western Balkans borderlands as far as the eye could see Tuesday as authorities cautiously lowered barriers and intensified efforts to cope with a human tide unseen since World War II.

Leaders of Slovenia deployed military units to support police on their overwhelmed southern border with Croatia, which delivered more than 6,000 asylum seekers by train and bus to the frontier in bitterly disputed circumstances between the former Yugoslav rivals.

With far too few buses available in Slovenia to cope, most people walked 9 miles on rural lanes past cornfields and pastures to reach a refugee camp, a challenge eased by sunny weather after days of torrential rain, fog and frigid winds.

On Slovenia’s frontiers with Croatia and Austria, aid workers toiled to erect enough tents and other emergency accommodation to shelter up to 14,000 travelers, more than five times the tiny nation’s previous official limit.

Interior Secretary of State Bostjan Sefic told reporters in the Slovene capital, Ljubljana, that the pressure on border security with Croatia had grown “very difficult with an enormous number of people.” He said Slovenia, an Alpine land of barely 2 million, needed much more help immediately from bigger EU partners to cope or the country might have to adopt border-toughening measures.

“If this continues we will have extreme problems. Slovenia is already in dire straits, an impossible situation,” Sefic said as lawmakers debated whether to increase the military’s powers to manage border security.

Slovenian President Borut Pahor said he expected his country to apply for emergency financial aid and border patrol reinforcements from EU partners.