Two boats filled with humanitarian supplies travelling from Mexico to Cuba have been located days after contact with them was lost in the Caribbean, according to organizers.

The boats were located by the Mexican Navy and the crews are safe, a spokesman for the Nuestra America Convoy said. He did not explain why the two boats - the Friendship and Tiger Moth - had disappeared.

They are among several vessels that have sought to carry supplies to the island nation since the US imposed an oil blockade in January, prompting a chronic fuel shortage.

The Mexican Navy has not commented on how it located the boats, which departed Isla Mujeres, in Mexico's easternmost state of Quintana Roo, on March 20, and had been due to arrive at their destination on Monday or Tuesday.

There are nine crew members - from Poland, France, Cuba, and the US - on board. The vessels are continuing their journey to [the Cuban capital] Havana, the Nuestra America Convoy spokesman said. The convoy remains on track to complete its mission - delivering urgently needed humanitarian aid to the Cuban people, he added.

Volunteers and non-governmental organizations have largely spearheaded efforts to deliver humanitarian aid to Cuba since US President Donald Trump's oil embargo on the communist-run country began.

The UN has warned Cuba faces dire supply shortages, with more than 50,000 surgeries canceled due to fuel supply constraints and aging infrastructure causing multiple nationwide blackouts.

Coupled with shortages of food and medicine, the situation has triggered rare public dissent in the form of street protests. Earlier in the week, the Cuban government celebrated and warmly received another boat that had carried 14 tonnes of humanitarian aid to the island.

The vessel, dubbed Granma 2.0 after the boat in which [late Communist leader] Fidel Castro returned to Cuba to launch its 1950s revolution, delivered solar panels, medicines, baby formula, bicycles, and food.

Since the US seized former Venezuelan President Nicolás Maduro in January and cut off the supply of oil from Venezuela - a staunch Cuban regional ally, Trump has turned his attention to the Caribbean island. He has threatened tariffs on any country supplying oil to Cuba and urged it to make a deal or face unspecified consequences.

The Cuban government has confirmed it is in talks with the US to resolve their differences, but has insisted that the political system of Cuba is not up for negotiation. On Friday, US Secretary of State Marco Rubio stated the system in Cuba must change for a better future.

You need to change the people in charge, you need to change the system that runs the country, and you need to change the economic model that it's following, Rubio told reporters.

The US Secretary of State denied there was a naval blockade around the island, pointing out that Cuba's fuel shortages stem from a lack of maintenance on old equipment.