Residents said on Thursday about 40 tanks and troop carriers had deployed about 7 km (4 miles) from Jisr al-Shughour. Activists and residents say the violence began after a mutiny among security forces who refused to fire at protesters.
Turkey's Red Crescent said it was setting up a second camp near the border to shelter people still crossing from Syria to escape the military build-up.
Turkish Foreign Minister Ahmet Davutoglu said on Thursday 2,400 people had already entered Turkey
"Jisr al-Shughour is practically empty. People were not going to sit and be slaughtered like lambs," said one refugee who crossed on Wednesday and who gave his name as Mohammad.