The bodies of the migrants, including a baby and two women, were found late on Saturday in two separate locations in the coastal town of Khoms, some 90km (55 miles) from Tripoli, the Red Crescent branch there said, Al-Jazeera reported.
Three other migrants were rescued, and search efforts were underway for others, it said.
“The bodies’ advanced state of decomposition indicates that the shipwreck happened several days ago,” a security official told AFP news agency, adding the toll could rise.
Images published by Libyan media outlets showed corpses lined up along the shore then placed in body bags.
The dead migrants likely drowned in recent shipwrecks off Libya, a key departure point for African and Asian migrants making desperate attempts to reach Europe.
About 1,500 migrants have drowned in numerous boat mishaps and shipwrecks in the Central Mediterranean route this year, according to the UN migration agency.
Migrants often endure horrific conditions in Libya before embarking northwards on overcrowded, often unseaworthy vessels that frequently sink or get into trouble.
The latest tragedy comes only days after 160 migrants died within a week in similar incidents, bringing the total number of lives lost this year to 1,500, according to the International Organization for Migration (IOM).
The IOM says more than 30,000 migrants have been intercepted in the same period and returned to Libya.
The European Union has cooperated closely with the Libyan Coast Guard to cut numbers of migrants arriving on European shores.