BARCELONA, Spain (AP) — Spain was searching for possibly dozens of migrants missing on three boats en route to the Canary Islands in the Atlantic Ocean, Spain’s maritime rescue service said Tuesday.

A Civil Guard airplane was searching for the boats near the islands of Lanzarote and Fuerteventura, off the northwest coast of Africa, the service said.

Earlier, the service said it was searching for 143 migrants in five boats but one returned to Dakhla on Western Sahara’s coast and another was rescued by the Moroccan Royal Navy. The service said it was now not sure how many migrants were on the three boats still missing.

Authorities were alerted about the missing boats on Monday afternoon.

Helena Maleno, of the human rights group Walking Borders, told The Associated Press that the migrants, including women and children, are believed to have departed from the northwest coast of Africa between Friday and Saturday.

Although the total number of sea crossings to Spain decreased by more than 50% in 2019, arrivals doubled via the dangerous Atlantic route to the Canary Islands, whose nearest point is about 100 kilometers (62 miles) from the African coast. According to the International Organization for Migration at least 210 people died on that route last year.