More than 250 migrants may have died when a boat sank a kilometre off the Libyan coast, a coast guard official said on Sunday.

"We believe there are still more than 250 bodies trapped underwater," coast guard official Mohammad Abdellatif told Reuters. "When we went underwater, we discovered that the boat is a lot bigger than we thought."

The boat sank late on Friday east of the capital, Tripoli. Thousands of migrants, mainly from sub-Saharan Africa, have crowded into rickety vessels in recent months in an effort to reach Italian shores. Many boats have been wrecked.

'Most of the bodies washed on the shores are still there because we don't have any resources to move them.'- Mohammad Abdellatif, Libyan coast guard

The total number reaching Italy has passed 100,000 in 2014, the Italian government said this week.

Libya is a major departure point for this journey, and human traffickers are exploiting the political chaos and lawlessness that has blighted the country since Moammar Gadhafi was toppled in an uprising in 2011.

Abdellatif said the coast guard had no resources for a rescue operation.

Libya migrant disaster

A shoe belonging to an African migrant floats in the waters near al-Qarbole, where the migrant ship sank. (Mahmud Turkia/AFP/Getty)

"Most of the bodies washed on the shores are still there because we don't have any resources to move them," he said. "We contacted everyone, the health ministry and the Red Cross, but no one came to help."

Libya is facing anarchy as the weak central government is unable to control armed groups who helped oust Gadhafi but are now fighting each other.

Ministries in Tripoli have been mostly closed since fighting between two groups escalated last month as staff, trying to escape rockets and street gun battles, only show up sporadically for work.