A shipwreck off Tunisia that claimed the lives of at least 40 African migrants has once again exposed the lethal risks of irregular sea crossings on routes to Europe, the UN migration agency said on Thursday.

The tragedy came amid concerns that worsening conditions for refugees and asylum-seekers in North Africa are pushing more families to embark on perilous journeys.

The boat, which had departed from the Tunisian village of Salakta, capsized shortly after setting off, killing nine women, 19 men and 12 children under the age of five, according to the UN International Organization for Migration (IOM).

An alert from a nearby fishing vessel led to the rescue of 30 people. Among the survivors were men, women and children from Cameroon, Ivory Coast and Guinea.

"This is one of the deadliest maritime incidents recorded along the north African coast this year," IOM said in a statement.

"It underscores the urgent need for coordinated action to prevent further loss of life along the Central Mediterranean route," the agency added.

According to IOM's missing migrants project, nearly 1,000 deaths and disappearances have already been recorded along the main route this year.

Since 2014, more than 25,000 people have died attempting the crossing from North Africa to Europe, making it the world's deadliest migration passage. The latest incident brings the total number missing in the wider Mediterranean region to more than 32,800.

Children have been among the most affected. At least 30 kids have lost their lives off Tunisia's coast this year alone, IOM said.