At least 94 people are dead and many are still missing after a horrific shipwreck in the Mediterranean Sea. Italian Coast Guard officials believe a fire broke out on board just off the coast of the Italian Island of Lampedusa and rescue efforts are underway. Authorities say the migrants are believed to be coming from Ghana, Somalia and Eritrae.NBC's Anne Thompson reports.

By Claudio Lavanga and Alexander Smith, NBC News ROME, Italy --

A boat carrying hundreds of migrants went down after catching on fire off Italy's southern coast Thursday, killing dozens and leaving at least 250 people missing, officials said.

Italian coast guard Commander Floriana Segreto told NBC News that at least 94 people had been confirmed dead with another 151 people rescued, adding that "lots more" people remained in the Mediterranean Sea off the Sicilian island of Lampedusa.

"It's horrific, like a cemetery, they are still bringing them out," Lampedusa Mayor Giusy Nicolini said, adding that the dead included at least one child and a pregnant woman.

Dead bodies are covered with sheets at the port of Lampedusa, Italy, on Thursday after a migrant boat sank.

Officials said there were between 400 and 500 migrants on the boat when it sank and Nicolini told Reuters the death toll was rising. The island is a popular landing point for migrants as it is just 70 miles from Tunisia's coast in North Africa.

Authorities said the victims included people from Somalia, Eritrea and Ghana. Pope Francis, who visited the island in July on his first papal trip outside Rome, "We pray to God for the victims of the tragic shipwreck off the coast of Lampedusa."

Later, in unscripted remarks after a speech in the Vatican he said: "The word that comes to mind is 'shame'….Let us unite our strengths so that such tragedies never happened again."

Coast guard ships and helicopters from across the region, as well as local fishing boats, were on the scene trying to find survivors, coast guard spokesman Marco Di Milla told The Associated Press.

U.N. High Commissioner for Refugees Antonio Guterres commended their “swift action.”

“At the same time, I am dismayed at the rising global phenomenon of migrants and people fleeing conflict or persecution and perishing at sea," he said. The vessel was thought to have left Libya, according to the U.N. refugee agency UNHCR.

Almost 500 people were reported dead or missing making the crossing from Tunisia to Italy last year, the UNHCR said.

Thursday's migrant shipwreck was one of the deadliest in recent times and the second one this week off Italy: On Monday, 13 men drowned while trying to reach southern Sicily when their ship ran aground just a few yards from shore. Reuters and The Associated Press contributed to this report. NBC News' Alexander Smith reported from London.