This photo shows the scene of a damaged building of Ukraine’s Danube port after a night drone attack in Odesa region. AFP

Russia attacked Ukraine's main inland port across the Danube River from Romania on Wednesday, sending global food prices higher as it ramped up its use of force to prevent Ukraine from exporting grain.

The drone attacks destroyed buildings in the port of Izmail and halted ships as they prepared to arrive there to load with Ukrainian grain in defiance of a de-facto blockade Russia reimposed in mid-July.

Ukrainian Deputy Prime Minister Oleksandr Kubrakov said the Russian attacks damaged almost 40,000 tons of grain which had been destined for countries in Africa as well as China and Israel.

"Moscow is waging a battle for a global catastrophe," President Volodymyr Zelenskiy said in his nightly video address. "In their madness, they need world food markets to collapse, they need a price crisis, they need disruptions in supplies."

Kubrakov, writing on Facebook, said the Danube ports' infrastructure had been "devastated".

"Ukrainian grain is indispensable for the world and cannot be replaced by any other country in the coming years," he wrote.

This handout photo shows a view of a damaged building at a Ukrainian port on the Danube in Odesa region. AFP

"The port of Izmail suffered the most damage, including the terminal and infrastructure of the Danube Shipping Company."

Russian state news agency RIA said the port and grain infrastructure hit was housing foreign mercenaries and military hardware. A naval ship repair yard was also targeted, it said.

RIA provided no evidence to back up its assertion and Reuters was not able to verify the report.

Video released by Ukrainian authorities showed firefighters on ladders battling a blaze high in a building covered with broken windows. Several other large buildings were in ruins, and grain spilled out of at least two wrecked silos.

There were no reports of casualties, Odesa regional governor Oleh Kiper wrote in a post on the Telegram messaging app.

Commercial ship-tracking data showed dozens of international ships halting and dropping anchor at the mouth of the Danube, many of them registered to arrive in Izmail in an apparent attempt to breach Russia's blockade.

The port, across the river from NATO-member Romania, is the main alternative route out of Ukraine for grain exports, since Russia's blockade halted traffic at Ukraine's Black Sea ports in mid-July.

Two industry sources told Reuters operations at the port were suspended. Seaport authority head Yuriy Lytvyn said on Facebook that repair work had already begun and the port infrastructure continued to operate.

Chicago wheat prices rose by nearly 5% on supply concerns after the attack, only to tumble later on Wednesday on strong Russian exports and signs Moscow may be open to reviving the Black Sea corridor deal.

Ukraine is one of the world's top grain exporters. Russia has attacked its agricultural and port infrastructure for more than two weeks after refusing to extend the Black Sea agreement, which had lifted its war-time blockade of Ukrainian ports last year.

Reuters