Vulnerable parts of the developing world, particularly in Africa, are at risk of sliding into famine as a result of the coronavirus pandemic, while humanitarian relief efforts are being hindered by lockdowns and travel restrictions, according to the UN.

Experts raised the spectre of unrest similar to that seen in 2007-08 when food price rises sparked riots around the world, destabilising fragile states and fuelling conflict in ways that are still being felt. They told the Guardian that the world could still avoid such a crisis, but time was running out.

“From a food security perspective, some places are very close to famine,” said Dominique Burgeon, the director of emergencies at the UN Food and Agriculture Organization (FAO). “The number of people on the verge of being extremely vulnerable was already very high. What we fear is that this number will further increase because of the impact of Covid-19 on food security.”

Swathes of the horn of Africa were already experiencing severe problems as swarms of locusts have been attacking crops over several countries, in the worst such outbreak for 70 years. Before the coronavirus struck, at least 20 million people were estimated to be in danger of acute food insecurity.

“The level of need was already extremely high. The one thing they did not need was one more shock. We are very concerned,” Burgeon said.

He said people in the rich world should not see food shortages arising from the coronavirus crisis as a problem for other people. If food shortages begin to bite, the impacts will reverberate across the globe.

He drew a parallel with the food price spikes in 2007-08, which triggered riots and unrest across north Africa and parts of the Middle East.

“This is a matter of international solidarity, and humanity, but also a matter of global security – to make sure the situation in some parts of the world does not create food riots,” he said.

Burgeon’s assessment was backed by Amer Daoudi, the senior operations director at the World Food Programme, which is serving 100 million people in dire need in Africa, Latin America and south-east Asia.

He also pointed to the food price jumps that occurred at the same time as the global financial crisis in 2007-08, and warned of a similar shock. Then, some countries exacerbated the price leaps by banning exports of staples such as wheat. He urged governments to avoid that this time.

“Remember in 2007 high food prices led to riots,” he said. “The world community needs to come together. We can avoid food shortages if we are able to support countries across the globe [that are vulnerable].”

Daoudi said food prices had not yet risen sharply as a result of the crisis, and international cooperation could keep food affordable and reaching areas where it is needed, but countries needed to come up with plans for achieving those aims.

“For the time being we are not seeing food prices rise internationally, but we are seeing food prices rise in local food markets,” he said. “We can avoid food shortages if we are able to supply countries across the globe. But if we interrupt the supply chain, food insecurity will definitely arrive.”

The WFP is organising a hub-and-spoke system of air cargo routes, creating “air bridges” to take food to some of the worst-affected regions as ground transport becomes impossible in lockdowns. But these efforts are also being hampered by travel restrictions.

“There are major bottlenecks in transport,” he said. “People also can’t access medical services.”

Daoudi urged countries to ensure food supply chains are kept open by maintaining free trade, avoiding food export bans and treating farm labourers as key workers.

The UN is concerned that if countries embrace protectionist measures, as some have done by restricting exports, then the threat of food shortages will rapidly become real. The chief economist of the FAO, Maximo Torero, told the Guardian last month: “The worst that can happen is that governments restrict the flow of food. All measures against free trade will be counterproductive.”

Funding is also a major issue. The WFP has requested $350m for its initial Covid-19 response, but so far only about $80m has been forthcoming, including £15m from the UK.

Last week several major multinational food companies including Unilever, Nestlé and PepsiCo warned that the coronavirus crisis could double the number of people at risk of hunger around the world. Leading economists and former political leaders have also called on the G20 to provide financial support to poor countries.

Burgeon said a swift response was crucial. In some of the vulnerable areas in Africa, he said, there were already armed militia and guerrilla groups. If coronavirus takes hold, people will be unable to work and tend to crops, and resources will be stretched further, fuelling greater instability.

Another complicating factor in some east African countries is that many people are pastoralists, depending for their livelihood on being able to move their livestock around. Travel restrictions will hurt them and may give rise to conflict.

The African Union will discuss the looming food crises at a special meeting with the FAO on Thursday.

Burgeon called for governments around the world to do more. “We need more international cooperation. We had humanitarian appeals before Covid-19, but now the needs are bigger, the funding gap is bigger,” he said. “Countries are mobilising but they need to accelerate.”

Daoudi echoed the call. “The world needs a new social contract, for us to come together as an international community,” he said. “We are in a race against time.”