A heartbreaking photograph of a drowned migrant baby in the arms of a charity worker has been released following a week in which 700 migrants were killed trying to cross the Mediterranean.

The baby, who appears to be no more than a year old, was pulled from the sea off the coast of Italy on Friday after a wooden boat capsized.

Forty-five bodies arrived in the southern Italian port of Reggio Calabria on Sunday aboard an Italian navy ship, which picked up 135 survivors from the same incident.

German rescue organisation Sea-Watch, operating a rescue boat in the sea between Libya and Italy, released the picture taken by a media production company on board, in a bid to convince European authorities to ensure the safe passage of migrants.

In an email, the rescuer, who gave his name as Martin, said he had spotted the baby in the water "like a doll, arms outstretched".

He said: "I took hold of the forearm of the baby and pulled the light body protectively into my arms at once, as if it were still alive ... It held out its arms with tiny fingers into the air, the sun shone into its bright, friendly but motionless eyes."

The rescuer, a father of three and by profession a music therapist, added: "I began to sing to comfort myself and to give some kind of expression to this incomprehensible, heart-rending moment. Just six hours ago this child was alive."

Like the photograph of the three-year-old Syrian boy Aylan laying lifeless on a Turkish beach last year, the image puts a human face on the more than 8,000 people who have died in the Mediterranean since the start of 2014.

Little is known about the child, who according to Sea-Watch was immediately handed over to the Italian navy.

Rescuers could not confirm whether the partially clothed tot was a boy or a girl and it is not known whether the child's mother or father are among the survivors.

Sea-Watch collected around 25 other bodies, including another child, according to claims from the crew seen by Reuters. The Sea-Watch team said it unanimously decided to publish the photo.

They said: "In the wake of the disastrous events it becomes obvious to the organisations on the ground that the calls by EU politicians to avoid further death at sea sum up to nothing more than lip service.

"If we do not want to see such pictures we have to stop producing them."

The organisation called for Europe to allow migrants safe and legal passage as a way of shutting down people smuggling and further tragedies.

At least 700 migrants are believed to have died at sea during the past week - the busiest week of migrant crossings from Libya towards Italy this year, the UN Refugee agency said on Sunday.

The boat carrying the baby left the shores of Libya near Sabratha late on Thursday, and then began to take on water, according to accounts by survivors collected by Save the Children on Sunday. Hundreds were on board when it capsized, the surivors said.

The baby's tragic death comes after it emerged that a woman migrant was decapitated in a horrific accident as a boat carrying 500 people started to sink in the Med on Thursday.

The vessel, which had no engine, was being towed by another smuggling boat - also with hundreds on board - when it started to take on water.

Survivors of the disaster claim refugees started to panic and jumped into the sea.

Others told how the Sudanese captain of the first boat then cut the tow rope which snapped back and decapitated a woman - though it is not clear which of the two boats she was on.

Hundreds drowned between Wednesday and Friday when their boats all overturned off southern Italy, according to the UN refugee agency.

Giovanna Di Benedetto, Save the Children's spokeswoman in Sicily, told AFP it was impossible to verify the numbers involved but survivors of Thursday's wreck spoke of around 1,100 people setting out from Libya on Wednesday in two fishing boats and a dinghy.

She said: "The first boat, carrying some 500 people, was reportedly towing the second, which was carrying another 500. But the second boat began to sink. Some people tried to swim to the first boat, others held onto the rope linking the vessels."

The Sudanese captain was arrested on his arrival in Pozzallo along with three other suspected people traffickers, Italian media reports said.