The economic crisis in Venezuela has turned millions of its citizens into refugees who are fleeing the country's hyperinflation and shortages in food and medicine. Now, it is having other spillover effects by dragging down an already ailing Cuban economy, two regional economists say.

A plunge in aid from Venezuela, along with a hardened trade embargo by the United States, has brought Cuba to its worst economic crisis since the post-Soviet depression in the 1990s, Carmelo Mesa-Lago, professor emeritus of economics and Latin American Studies at the University of Pittsburgh, and Pavel Vidal Alejandro, associate professor economics at the Pontifical Xavierian University in Cali, Colombia, write in their report.

"The Venezuelan shock in the Cuban economy is not something that is bound to happen in the near future, but has already been happening since 2015," say the authors of the working paper published by Real Instituto Elcano, a think tank in Madrid that focuses on international affairs.

Venezuela went from being one of the richest countries in Latin America, with one of the world's largest oil reserves, to facing the worst economic crisis in its history. Today, the country has debts of about $200 billion, most of which the government has defaulted on. Its economy is performing worse than Haiti, Honduras and Nicaragua, the authors add.

Trade between Cuba and Venezuela has dropped from $8.5 billion in 2012 to $2.2 billion in 2017. The exports of goods fell from $2.4 billion to $375 million in the same time period, while imports decreased 70%.

Cuba imports about two-thirds of its food at an annual cost of more than $2 billion, according to a report by The Associated Press. But the collapse of Venezuela's state-run oil company has led to a nearly two-thirds reduction in fuel shipments that Cuba had used for both power and to earn hard currency.

Shortages in goods in Cuba have been common for years, but the government in May announced rationing of chicken, eggs, rice, soap and other products. In June the U.S. announced new restrictions on U.S. travel to Cuba, a move that many on the island nation say will adversely affect the economy.

Venezuela has been Cuba's greatest ally since the fall of the Soviet Union at the end of 1991 that caused one of the greatest economic crises in Cuba since the Great Depression. Cuba slowly replaced the Soviet help with a closer relation with Venezuela beginning in 2000, when Cuban's President Fidel Castro and Hugo Chavez, his Venezuelan counterpart, signed a cooperation agreement that made Venezuela export 53,000 oil barrels at below-market prices in exchange for Cuban services in areas such as health, education and sports.

"This was a change from the previous Cuban practice of sending professionals for free to countries that needed them," the authors say.

For the new economic crisis end, Cuba must accelerate and deepen the structural economic reforms that began to be implemented under Raúl Castro, Mesa-Lago said on Thursday at a conference at Inter-American Dialogue in Washington, D.C.