Bulgarian border police officers have discovered 129 migrants in a refrigerated truck at the Kapitan Andreevo crossing at the Bulgaria-Turkey border.
The migrants were "in good health" at the time, the Interior Ministry has said.
It has added none had proper documents.
Of them, 38 were men, 33 women, and 58 children. All were hiding behind bottles of water.
Bulgaria has embarked over the past weeks on a series of operations to prevent people smuggling, with dozens arrested across the country every day, amid increased pressure on the Turkey border. This week's peak was Saturday, with 495 migrants and 16 suspected smugglers detained.