Bulgaria has reopened navigation on its stretch of the Danube after almost a month of suspended shipping after the river froze over, the transport ministry said Friday.

"Navigation was restored all along the Bulgarian part of the Danube river, after improved conditions," the ministry said in a statement.

All ports along Bulgaria's 450-kilometre (280-mile) stretch of one of Europe's key waterways are now open for business again, it added.

The only exception were the two northeastern ports of Silistra and Tutrakan, where massive ice floes moving downriver damaged port facilities over the past days.

The surface waters of the Danube froze completely for the first time in over 20 years in February, halting all river traffic along the 2,860-kilometre (1,780-mile) river.

As parts of the Danube are still blocked, the ministry warned all boat captains on Friday "to navigate with heightened caution and at their own risk".