Hundreds of migrants have been reported missing and at least 10,000 more have been rescued in the Mediterranean and brought to Europe in the last week, highlighting the scope of the challenge facing the European Union and further exposing weaknesses in its migration policy. Here's a look at the situation:

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WHY PEOPLE ARE COMING: Some are fleeing conflict or persecution and others are looking for a way out of poverty. They come to Europe from countries including Eritrea, Niger, Syria, Iraq and Somalia. Many claim to be Syrian to improve their chances of staying. Right now, the weather is good, so smugglers are bringing over more people willing to spend thousands of euros apiece to risk their lives on poorly maintained, overcrowded boats.

BY THE NUMBERS: Almost 280,000 people, some refugees escaping conflict, entered the EU illegally last year, a 138 percent increase over 2013. The International Organization for Migration estimates that at least 3,279 died in the Mediterranean in 2014. The U.N. refugee agency predicts that some 500,000 more people will flee Syria alone in 2015.

HOW THEY GET TO EUROPE: The main route is through conflict-torn Libya, where there are no effective border controls and smugglers are operating with near impunity. They have developed a well-oiled operation of acquiring boats and sending the migrants off with a satellite phone to make a call to Italian or Maltese authorities to come to their rescue once they're at sea.

LIFE-SAVING EFFORTS: Under international law, the nearest vessel to any emergency must try to come to the rescue. These are often civilian ships — including ferries, cargo or private vessels — or national coast guards. The EU's border agency Frontex has ships and planes in the Mediterranean but its job is to monitor Europe's borders and migration flows, not save lives. Before the latest Frontex effort, called Operation Triton, there was an Italian emergency search and rescue effort called Mare Nostrum, but it was expensive and politically unpopular in Italy. It ended late last year.

THE FATE OF PEOPLE WHO MAKE IT TO EUROPE ALIVE: Migrants picked up at sea are supposed to be interviewed and have biometric and other data recorded as soon as they arrive. They are taken to reception centers where they can apply for asylum or some other form of legal status. Asylum can only be granted in the European country where they first land. Many migrants who make it undetected never register themselves, instead heading immediately for train stations to travel to northern European destinations where they can find jobs or apply for asylum. Some are given temporary permits allowing them to stay while their applications are processed. Some are invited to return to their countries of origin voluntarily, while others are returned forcibly.

WHAT EUROPE IS DOING: The EU foreign and interior ministers were holding an emergency meeting Monday to address the crisis. European Union leaders will hold an emergency summit Thursday.