G7 industralised nations will tackle a looming global food crisis at talks starting Thursday, host Germany said, stressing that the world's poorest must be shielded from the effects of Russia's invasion of Ukraine.

"We as the strongest industrialised democracies have a special responsibility" to help poorer nations weather the food and energy squeezes caused by the war, Foreign Minister Annalena Baerbock said at the gathering in the northern German resort of Wangels.

The foreign ministers from the Group of Seven industrialised nations will not only discuss "how we can continue to support Ukraine but also how we can help the poorest people in the world in this situation", Baerbock said.

"It is not only about grain but also about energy supply worldwide," she added.

Before the war, Ukraine was the world's bread basket, exporting 4.5 million tonnes of agricultural produce per month through its ports -– 12 percent of the planet's wheat, 15 percent of its corn and half of its sunflower oil.

But with the ports of Odessa, Chornomorsk and others cut off from the world by Russian warships, the supply can only travel on congested land routes that are painfully inefficient.

Currently, train waggons and containers are backed up at the border with mountains of grain sitting in silos in Ukraine needing to move before the next harvest.

This means food is not getting to "people in the world who urgently need it, above all in African countries and in the Middle East", Baerbock said. 

"This looming food crisis is being exacerbated by the global effects of climate change. And that is precisely the aim of the Russian president -- to use this crisis... to divide the global community," she added.

The foreign ministers are meeting over three days in Germany, which currently holds the presidency of the G7.

The other members of the group are Canada, France, Italy, Japan, Britain and the United States.

The war in Ukraine is set to be the main topic on the agenda, with Ukrainian and Moldovan foreign ministers Dmytro Kuleba and Nicu Popescu also on the guest list.