A boat carrying around 400 refugees is feared to have sunk in the Mediterranean sea, the fourth migrant boat to sink this week.

Migrants rescued from two boats off the coast of Italy told humanitarian workers they saw another vessel sink that was not picked up by coast guards, according to Save the Children.

Three vessels carrying migrants have already been confirmed as sunk or capsized in the past week. More than 60 bodies have been recovered, including three children, with hundreds more said to be missing.

Survivors from the other reported vessels said in interviews on Saturday that a fourth boat had been seen. According to refugee witnesses, the ship, along with another fishing boat and rubber boat, left Sabratha in Libya late on Wednesday night.

The rubber boat had its own motor, but the smaller fishing boat did not and was towed by the larger fishing vessel, which is said to have held around 500 more people.

Eventually the smaller boat began to take on water and its tow line was cut by order of the larger boat’s captain. The smaller boat is then said to have sunk with most of its passengers, according to interviews heard by Save the Children workers.

“There were many women and children on board,“ Giovanna Di Benedetto, spokeswoman for Save the Children, told Reuters. ”We collected testimony from several of those rescued from both (the rubber and fishing) boats. They all say they saw the same thing.“

Police in Ragusa have detained a man suspected to be the captain of the larger boat, state news agency Ansa have reported.