A boat carrying migrants capsized on Wednesday in the Mediterranean north of Libya, and hundreds are feared dead, officials said, NBC News reported.
Medecins Sans Frontieres said in a statement that its vessel Dignity I was on the scene.
"There could have been up to 700 people on board at the time of the incident," the organization said in a statement. It added that there were "several confirmed deaths at the scene."
Italian ships and an Irish naval vessel were assisting in the rescue operation.
Over 2,000 migrants have died so far this year trying to cross the Mediterranean, according to the International Organization for Migration.