Cuban President Miguel Diaz-Canel expressed concern on Friday for two missing sailboats carrying nine people that were bound for Cuba with humanitarian aid.

The Mexican navy said on Thursday night that they were searching for the boats, which departed from Isla Mujeres in southern Mexico on March 20.

The disappearance comes as an increasing number of countries and aid organizations send shipments of aid to Cuba as a U.S. fuel blockade causes crippling blackouts and pushes the Caribbean nation to the brink of collapse.

“From our country, we are doing everything possible in the search and rescue of these brothers in struggle," Diaz-Canel said.

So far, naval authorities have received no communication or confirmation of the vessels’ arrival in Cuba, which had been expected between Tuesday and Wednesday of this week.

On Friday, the organization Nuestra America Convoy, said that based on the speed of the vessels reported to the Cuban maritime authorities, the boats in Havana should arrive between Friday and Saturday. The organization made an open call for any information or sightings of the boats.

The captains and crews are experienced sailors, and both vessels are equipped with appropriate safety systems and signalling equipment.

"We are cooperating fully with the authorities and remain confident in the crews’ ability to reach Havana safely," the organization said in a statement.

A first vessel from the Convoy Nuestra America, carrying 14 tons of food and medicine, 73 solar panels and about a dozen bicycles, arrived in Havana on Tuesday.

As part of the search efforts, the Mexican navy alerted naval commands in Isla Mujeres and Yucalpeten, as well as naval search, rescue and surveillance stations. It also established coordination with maritime rescue coordination centers in Poland, France, Cuba, and the United States, along with diplomatic representatives from the countries of origin of those on board.

Search operations involve navy vessels and Persuader-type aircraft, which are carrying out maritime and aerial search patterns along the estimated route between Isla Mujeres and Havana. The efforts take into account possible course changes, as well as prevailing weather conditions and ocean currents in the region.