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By Cassandra Vinograd and Claudio Lavanga

Hundreds of migrants are feared dead after a vessel journeying across the Mediterranean Sea shipwrecked off the coast of Libya, rescue coordinators said Wednesday.

As many as 700 people may have been on the boat when it capsized, according to medical aid group Medecins Sans Frontieres, which sent its vessel, the Dignity I, to help.

Complete Coverage: Europe's Migrant Crisis

Italian Coast Guard officials told NBC News that about 400 migrants were saved, while at least 25 others were found dead. Seven ships are assisting in the recovery efforts, about 68 miles northwest of Tripoli.

Ireland's Navy also confirmed to NBC News that one of its vessels, the LÉ NIAMH, was assisting in the rescue operation. Officials added that a significant loss of life was expected from the accident.

Related: U.N. Says Record-Setting 137,000 Cross Mediterranean

"Due to circumstances unknown, the vessel capsized and the LÉ NIAMH immediately commenced rescue operations, deploying all available assets including (inflatable boats) and life rafts," Irish officials said.

Over 2,000 migrants have died so far this year trying to cross the Mediterranean, according to the International Organization for Migration. It said approximately 188,000 migrants have been rescued in the Mediterranean so far this year.

Migrants sit in inflatabletable boats during rescue operations by the Irish Navy patrol vessel "Le Niamh" off the Libyan coast on Aug. 5. A major rescue operation is underway after a boat with some 700 migrants capsized off Libya. Around 200 migrants are feared dead.IRISH DEFENSE FORCES / EPA
Emmanuelle Saliba, Euronews and F. Brinley Bruton contributed.