More than 45 bodies have been recovered after a suspected people smuggling vessel capsized on a lake in northern Malawi earlier this week, police said on late Thursday. An unknown number of other people are believed to be missing and feared dead.

The accident is believed to have happened on Monday evening when the overloaded boat capsized on Lake Malawi as it was traveling from neighboring Tanzania. It is believed to boat was attempting to smuggle as many as 60 illegal immigrants from Somalia and Ethiopia into Malawi.

The incident was not discovered until Tuesday morning when locals in Karonga District noticed bodies floating on the lake, which is located between Malawi, Mozambique and Tanzania and is the southernmost lake in the East African Rift system. Rescue workers soon discovered the vessel which was upside down in the water.

It remains unclear how many people were on the boat, but local authorities estimate the number to be around 60. Malawi Police Service spokesman Dave Chingwalu said 44 bodies were recovered as of 3 p.m. local time on Thursday, and three more were recovered shortly after. It is unknown if some of the illegal immigrants may have reached land safely and fled before the incident was discovered.

Chingwalu added that police have arrested three Malawians on suspicion of organizing the people smuggling in collaboration with contacts in Tanzania. It is believed most of the victims are from Ethiopia, although some of the victims may have also come from Somalia. The spokesman said more arrests were expected soon.