Survivors from a boat which capsized off the Egyptian coast on Wednesday have told the BBC that hundreds of people may have drowned.

The boat was carrying about 550 migrants when it capsized eight miles (12km) off the coast, they say.

Authorities have rescued 163 people and recovered 42 bodies so far off the port city of Rosetta.

Four suspected traffickers have been detained, according to the AFP news agency.

They are accused of involuntary manslaughter and human trafficking, judicial officials were reported as saying.

The incident came after the EU's border agency warned that increasing numbers of Europe-bound migrants are using Egypt as a departure point.

The UN says that more than 10,000 people have died crossing the Mediterranean towards Europe since 2014.

The boat was kept off the coast for five days as more and more migrants were brought on board, survivors told the BBC's Orla Guerin in Rosetta. Just over 100 of those rescued were Egyptians.

Migrants were charged extra if they wanted to wear life jackets, she reports.

The boat is said to have capsized after a final group of some 150 people were crammed on board.

Authorities have been accused of failing to send help fast enough.

"Anyone who was saved here, was saved by the local fishing boats," fisherman Abdelrahman Al-Mohamady told the Reuters news agency.

The victims so far include one child, 10 women and 31 young men, an official in Rosetta told AFP.

The boat was transporting Egyptian, Syrian, Sudanese, Eritrean and Somali migrants. Many survivors are now being held in police custody.

Rescuers are focusing their efforts on the boat's cold storage room, where it is believed around 100 people took refuge during the capsize.

Some teenage Egyptian survivors, huddled together in the basement of a police station, told the BBC they were trying to reach Italy to find work.

The Egypt office of the International Organization for Migration (IOM) say high birth rates and few job opportunities are pushing young Egyptians into taking the risk of a dangerous sea voyage.

Authorities say Egyptians in police custody will soon be released but foreign nationals will be held for a few days for questioning as to how they entered the country.