Russia's invasion has forced Ukraine to reroute its grain exports, as its six major Black Sea ports remain under a blockade. The standoff has left millions at increased risk of starvation. A deal is being discussed to allow the resumption of exports but it may take months until the ports re-open. The BBC's Nick Thorpe has seen the bottlenecks in Hungary and Romania.

"You have to understand this as a logistical chain, and there are so many weak links," says Capt Botond Szalma. In his office in Budapest, a chart of the Black Sea, the Danube river, and the whole eastern flank of Europe, from Poland to Turkey, is spread out on the table.

He is a third-generation ship's captain; his grandfather and father both moved grain on the Danube. "We're trying to catch up on 30 years of disastrous neglect of the rail infrastructure in the whole region, including Hungary," says Capt Szalma, who is also executive vice-president of the Federation of National Associations of Ship Brokers and Agents (Fonasba).

These problems, from lack of storage to inadequate transport, are now being felt as the Russian blockade continues.

Ukraine is one of the world's largest grain producers. Since Russia invaded the country in February, new ways had to be found for Ukraine to export 20m tonnes of wheat left from the 2021 harvest, and the expected 60m tonnes of this year's harvest.