Truck traffic between Bulgaria and Romania was halted Tuesday after a huge hole opened on a bridge over the Danube that carries the main cross-border route between the two countries.
The gap in the road section of the bridge -- which also includes a rail section -- revealed the structure's steel reinforcements and necessitated urgent repair work, Bulgaria's road agency said.
The agency banned trucks weighing over 10 tonnes (22,000 pounds) from crossing the bridge. Lorries were redirected to ferry lines.
The agency said heavy trucks will be allowed to use the bridge again from Saturday, but that access will remain restricted.
Bulgarian media reported that huge queues of trucks had already formed at the closest ferry ports of Svishtov and Silistra on the Bulgarian side, as the boats' small capacity could not cope with the increased traffic.
Car and rail traffic over the bridge continued as normal.
The 2.8-kilometre (1.7-mile) structure, which spans the Danube between the Bulgarian city of Ruse and the Romanian city of Giurgiu, is the only one along the River Danube, which forms 470 kilometres of the border between the two countries.
Built in 1954, it has only been repaired three times since then.
EU aid funds have helped Bulgaria and Romania build a second Danube bridge between Vidin and Calafat, further west, but it will only open in May.