Hormuz accounted for a fifth of global oil shipping before the US and Israel launched strikes against Iran, which prompted Tehran to effectively shut down the strait to tanker and cargo traffic.

A third of the world's fertiliser supply also passed through the strait before the war, and officials have warned that farmers could face shortages during the summer growing season.

The Rome-based FAO said there should be more attention on alternative land and sea routes, including across the Arabian peninsula to the Red Sea.

It also called for countries to avoid export restrictions on energy and fertilisers and to exempt food aid from trade curbs.

The time has come to "start seriously thinking about how to increase the absorption capacity of countries, how to increase their resilience to this choke", the FAO's chief economist Maximo Torero said in a podcast published Wednesday.

In a statement, the agency said the Hormuz blockage was "not a temporary shipping disruption" but "the beginning of a systemic agrifood shock".

It warned a full-blown global food crisis could come within six to 12 months.

"The shock is unfolding in stages: energy, fertiliser, seeds, lower yields, commodity price increases, then food inflation," it said.

The FAO said its global food price index had risen for three consecutive months since the start of the conflict.