Greek authorities began an operation at dawn on Tuesday to gradually evacuate the country's largest informal refugee camp of Idomeni on the Macedonian border, blocking access to the area and sending in more than 400 riot police. The government has pledged that police will not use force, and say the operation is expected to last about a week to 10 days. Police said 13 buses carrying a total 609 people left Idomeni in two batches, heading to new refugee camps in northern Greece. No violence was reported. The camp, which sprang up at an informal pedestrian border crossing for refugees and migrants heading north to Europe, is home to an estimated 8,400 people — including hundreds of children — mostly from Syria, Afghanistan and Iraq. At its peak, when Macedonia shut its border in March, it housed more than 14,000, but numbers have declined as people realized the border was shut and began accepting authorities' offers of alternative places to stay. In Idomeni, most have been living in small camping tents pitched in fields and along railroad tracks, while aid agencies have set up large marquee-style tents to help house people. Greek authorities have been sending in cleaning crews regularly and have provided portable toilets, but conditions have been precarious at best, with heavy rain creating muddy ponds. In recent weeks, the camp had begun taking on an image of semi-permanence, with refugees setting up small makeshift shops selling everything from cooking utensils to falafel and bread. More than 54,000 refugees and migrants have been trapped in financially struggling Greece since countries further north shut their land borders to a massive flow of people escaping war and poverty at home. Nearly a million people have passed through Greece, the vast majority arriving on islands from the nearby Turkish coast. In March, the European Union reached an agreement with Turkey meant to stem the flow and reduce the number of people undertaking the short but perilous sea crossing to Greece, where many have died after their overcrowded, unseaworthy boats sank. Under the deal, anyone arriving clandestinely on Greek islands from the Turkish coast after March 18 faces deportation to Turkey unless they successfully apply for asylum in Greece. But few want to request asylum in the country, which has been struggling with a deep, six-year financial crisis that has left unemployment hovering at around 24 percent. Journalists were barred from the camp during the evacuation operation, stopped at a police roadblock a few kilometers (miles) away. Twenty buses carrying various riot police units were seen heading to the area while a police helicopter observed from above. An estimated 700 police were participating in the operation. Greek authorities are also eager to reopen a railway line — the country's main freight train line to the Balkans — that runs through the camp and has been blocked by protesting camp residents since March 20. A spokesman for Greek transport companies said Tuesday that the 66-day closure has cost transporters about 6 million euros. Speaking in Idomeni, Anastassios Saxpelidis said he hoped trains could start running again at the end of this week. He said 200 empty freight carriages are in Greece, waiting to take on goods further north, while 40 loaded carriages are stuck in Macedonia and seven trains in Hungary — all destined for Greece.