They call him "Presidente" and he is greeted like a rockstar, but in truth, Juan Guaido has a big task ahead of him.

Key points: Opposition leader Juan Guaido declared himself president of Venezuela in January

Opposition leader Juan Guaido declared himself president of Venezuela in January He has been backed by more than 50 countries, including the US and Australia

He has been backed by more than 50 countries, including the US and Australia Venezuela is experiencing the worst economic collapse in a country not at war in 45 years

The charismatic 35-year-old with the enormous smile is taking on Nicolas Maduro, and the incumbent Venezuelan President is not inclined to make it easy for the young usurper.

A former student politician, Mr Guaido was elected as a legislator in 2015 and only became the head of the opposition-held National Assembly last year.

Just days into his new post, he launched his challenge to Mr Maduro, declaring himself president of Venezuela in January after widely disputed elections — something that is allowed under the country's constitution.

When he arrived to meet supporters at an event in Valencia about two hours drive from Caracas, it was a free-for-all as journalists and photographers jostled with fans seeking handshakes and selfies.

Dressed in a sharp blue suit, Mr Guaido sailed through it with his trademark grin intact and then sat for two hours on stage as speaker after speaker listed the litany of issues affecting the country.

We've spent a week trying to catch up with him. Security concerns mean he's been skipping from safe house to safe house, and despite his groomed appearance, apparently bathing out of a bucket. He changes his office location regularly too, and his team is reluctant to telegraph his movements, even to the press, for fear he'll be arrested, or worse.

Venezuelan opposition leader Juan Guaido has been recognised as the country's rightful interim ruler by more than 50 nations. ( Reuters: Ueslei Marcelino )

Not long ago, oil-rich Venezuela was Latin America's wealthiest nation.

But the oil price crash in 2014 exposed economic mismanagement in the extreme.

Socialist leader Hugo Chavez was adored for his social programs for the poor. But years of government largesse left nothing in the bank, and Mr Maduro has been unable to deal with the consequences of what he inherited when Mr Chavez died.

Oil, power, water and telecommunications utilities were stacked with cronies and had not been properly maintained. There are constant blackouts and disruptions.

When the currency crashed and the Government tried to prop it up by printing money, inflation exploded.

Venezuelans starve as country's economy collapses

Venezuela now has the highest inflation in the world.

People can't afford enough food, the health system has all but collapsed and almost 4 million people have fled the country.

It is a disaster.

Some children are relying on soup kitchens to eat as the price of food surges. ( ABC News: Niall Lenihan )

In fact, it is the largest economic collapse in a country that is not at war in 45 years.

"Today Venezuela is not just a problem for Venezuela," Juan Guaido told the ABC.

"There are 4 million Venezuelans who have left the country and the projections say if we keep the same flow this year, we will reach 7 million," he said.

Mr Guaido estimated that between 2017 and 2019, 20,000 children under the age of one had died due to a lack of food.

Official figures on infant and maternal mortality, escalating diseases and the general deterioration in the health of the population are difficult to find, in part due to the collapse in services, as well as government censorship.

Anything that portrays the Government in a negative light can also attract retribution for those who share or publish it.

However, the little data that is available, including a report from Human Rights Watch and America's John Hopkins University, paints a disturbing picture.

Malnutrition is rife and malaria is out of control. Measles, diphtheria and tuberculosis are re-emerging. The return of polio is a risk.

Many medications are unavailable or too expensive, but hospital patients and their families have to somehow source their own due to lack of in-house supplies.

During a week in Venezuela, both in the slums of Caracas and in rural areas, every family the ABC met was struggling for food.

Although there are shortages of some items, the problem is not supply but the cost of buying food.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 16 seconds 1 m 16 s Hyperinflation in Venezuela is leading to starvation

Nothing has a fixed price because hyperinflation means the cost of an item can change within hours.

For people on the minimum wage of less than $AU10 per month, something that was affordable in the morning may be out of reach by the afternoon.

Mr Guaido and his loose opposition coalition want Mr Maduro out, and despite a failed attempt at an uprising to eject him in April, he said they are not giving up.

US secretary of state Mike Pompeo has expressed concern that the fragmented opposition alliance might fall apart, but the young politician is certain he can hold it together.

"No doubt," he said.

He has been backed by the US, Australia and more than 50 other countries.

"What the international community has done so far, I think, is very important," he said.

"The recognition of our constitution and of me as interim president — Australia did that too and we're thankful for that — the sanctions, the protection of the assets," he said.

However, Mr Guaido urged the international community to continue putting pressure on the Maduro Government.

"A dictatorship will not willingly leave. Only through pressure, only through international and local support will we be able to generate a real alternative to escape from this conflict," he said.

Maduro rejects blame for Venezuela's economic woes

Nicolas Maduro has blamed his enemies for Venezuela's economic woes. ( Reuters: Adriana Loureiro )

The Maduro Government has rejected the premise that mismanagement and corruption are at the core of Venezuela's problems.

Nicolas Maduro says US sanctions are putting the squeeze on the economy, and he has attacked the Trump administration for interfering in domestic politics.

Certainly, the United States has form on this front.

A Harvard study found the US was behind at least 41 of 162 power changes via military coup in Latin America between 1900 and 2006.

Mr Guaido said declaring himself the president of Venezuela was legitimate under the constitution after sham elections because he is seeking a transitional government followed by a new, free and fair poll.

He denied that the attempt to oust Mr Maduro on April 30 had caused his campaign to stall.

Venezuela has been hit by multiple protests since Mr Guaido declared himself president in January. ( Reuters: Garcia Rawlins )

"We have mobilised big crowds in the countryside and we have an average of 39 protests each day in Venezuela," he said.

"Momentum is probably one final step to get rid of the dictatorship, but we are a majority and it's not just me saying it. It is reflected at the polls."

If or when Mr Maduro does eventually go, it is possible that Mr Guaido won't even be the opposition candidate for the presidency at a future election.

For many Venezuelans he remains an outsider, a policy-driven politician who has not been seen as presidential material until now. Although he has attracted international backing, he remains a relative newcomer to national politics.

Many are still struggling to see him as the leader, because he's so young, and because there are other opposition figures who have more seniority within the opposition movement.

When asked about his future prospects, he was cagey.

"The most important thing right now is the cessation of the usurpation, to contain the tragedy of the humanitarian emergency, to contain the catastrophe, to create the transition and to have free elections," he said.

"What I can say today is that we will have one candidate from the opposition who will be elected by consensus or in primary elections, but right now my role is to facilitate."

It may be a politician's answer.

But timing is everything, and Juan Guaido has that on his side, amid a national crisis and a hungry, desperate population wanting change.