More than 100 migrants are missing after their vessel sank off Libya's coast soon after it set off to cross the Mediterranean. Dozens of bodies have washed up on the shore, local Libyan authorities said.

The vessel went down over the weekend near the town of Zuawrah, west of Tripoli. Around 70 migrants, mostly from Syria and sub-Saharan Africa, were rescued and around 30 bodies have been recovered, authorities said.

"According to the survivors there were more than 250 illegal immigrants on the ship, most of them from Syria or sub-Sahara," an official at the press center for the local town government said.

There was no immediate reaction from the Libyan government.

Libya, whose fragile government has been unable to impose its authority on large parts of the country, has become an increasingly common takeoff point for illegal migrants trying to cross the Mediterranean to Europe.

The United Nations said in August that nearly 2,000 people fleeing Africa and the Middle East have drowned in the Mediterranean this year, most of them in the past three months as they tried to reach Europe from Libya.