Updated 8pm

Four women are reportedly unconscious and others are ready to jump overboard as a fishing boat carrying 400 migrants continues drifting between Malta and Greece for days, an NGO said on Thursday. 

"Everyone is desperate. How much longer must they wait? Authorities are violating the law," the migrant hotline NGO Alarm Phone said in a tweet, citing Italy and Malta.

 It added that the Italian coast guard had informed it that the coast guard was on its way eight hours ago. Instead of coordinating rescue, the Maltese authorities instructed a cargo ship to just give it fuel, the NGO has claimed. 

The AFM, which handles rescue operations, has given no comment. 

The migrants are believed to have set off from Tobruk in Libya and the boat has been drifting between Malta and Greece in Malta's search and rescue zone. 

An alert about its presence was first raised by migrant support group Alarm Phone.

On Sunday, Sea Watch International said its spotter plane had found the boat, with 400 people in distress.

It said that two merchant ships were located nearby but they had been ordered not to carry out a rescue.

"Instead, one was asked by Malta to only supply the boat with fuel," it said.

On Monday morning it reported that the boat had indeed been supplied with fuel and water, "but has not rescued it following orders from Malta." The supplies were provided by a merchant ship.

The boat, it said, is struggling in 1.5m waves and in 'huge danger'.   

Later it reported that the Italian coast guard had set out to rescue the migrants.

"Malta must be held accountable for the ruthless ignorance. Preventing the rescue of people for political calculation must be punished!" it insisted.

In an update, Italian authorities issued a press statement saying the boat was in Italy's search and rescue zone and that rescue operations were under way. 

The vessel was located about 170 miles south-east of Sicily’s Capo Passero, they said, and was being assisted by the coast guard ship Diciotti. Two merchant vessels were also on hand to provide assistance, they confirmed.

19 migrant boats in a day

Sea Watch said Easter was not a quiet time in the Mediterranean, with its reconnaissance aircraft finding 19 boats in distress, "many of which are probably still out there."

Alarm Phone, which uploaded a map showing the location of the boat, said on Sunday that the boat was drifting and one of the decks was taking in water. Three people had jumped overboard, with one of them eventually falling unconscious.

The location of the boat pinpointed by Alarm Phone.

"EU SAR authorities know they are there and risking to die. What are they waiting for?" it said.

It also said the master of the boat had "left" and there was nobody who could steer the boat. Several people required medical attention, including a child, a pregnant woman and a person with a physical disability.  

Migrants feared drowned between Tunisia, Italy

On Sunday, German aid group ResQship said at least two migrants died and around 20 others were missing after their vessel sank in the Mediterranean between Tunisia and Italy.

The group's ship, the Nadir, rescued another 22 people and took them to the Italian island of Lampedusa.

Among those rescued were men, women and children from Cameroon, Ivory Coast and Mali.  A pregnant woman was among those saved, while the boat's crew also recovered the bodies of two men.

In all, around 40 migrants were on the boat when it left Sfax in Tunisia. 

The migrants are believed to have paid 3,000 Tunisian dinars (about $980) each to get passage on the vessel.

Describing their operation earlier Sunday on Twitter, ResQship said that when they arrived at the scene of the wreck, the migrants had already been in the water for about two hours. 

"This is an unspeakable tragedy that could -- and should -- have been prevented by a humanitarian approach to migration instead of barb-wiring the European borders," the group added.

Last week, 440 people were rescued by an NGO's ship from the sea between Malta and Libya in an area within the Maltese search and rescue zone. They were taken to Italy. The migrants had spent four days at sea, battling a storm in a boat that lacked food and water, Doctors Without Borders (MSF) said.

Thousands land in Lampedusa

In the last few days, thousands of migrants have landed on Lampedusa, which lies only about 150 kilometres (90 miles) from the Tunisian coast.

This incident is the latest in a series of disasters in the Mediterranean Sea, where dozens of migrants attempting the crossing have drowned and dozens more have had to be rescued from flimsy vessels. 

Italy has been complaining for some time about the number of migrants arriving on its shores.

Almost 28,000 migrants have arrived in Italy since the beginning of the year, according to the UNHCR, which also notes that Malta has rescued one person.