The boat, which departed from Tobruk in Libya, called support service Alarm Phone overnight to report the situation.
People on board are panicking and several need medical attention, Alarm Phone said. Passengers include a child, a pregnant woman and someone with a physical disability, they added.
German NGO Sea-Watch International tweeted that those on board were in “imminent danger of death” and called on the EU to act.
The vessel ran out of fuel and its lower deck is reportedly overflowing with water.
The captain has left and there is “nobody who can steer the boat”, Alarm Phone said.
The boat is now in the Maltese Search and Rescue area.
Sea-Watch International said it had found the boat with two merchant ships nearby.
It said the Maltese authorities had ordered the ships not to carry out a rescue and that one of them was just asked to supply it with fuel.
