Albania's Defense Ministry said that 21 were killed and more than 600 injured following pre-dawn earthquake, the most powerful that hit the country in the last 30 years.

The government declared an official day of mourning for Wednesday, with Albanian flags on official buildings to fly at half-staff. Neighboring Kosovo, which has an ethnic Albanian majority population, also declared Wednesday a mourning day.

Schools would remain closed until Monday, as Thursday and Friday were national holidays.

The country's soccer federation announced all matches would be cancelled for the rest of the week.

President Ilir Meta called on the Cabinet to ask for international assistance and called for solidarity with the affected population.

The magnitude-6.4 quake was felt across the southern Balkans and was followed by multiple aftershocks, with several above magnitude 5.

The quake in Albania collapsed at least three apartment buildings while people slept, and rescue crews were working to free people believed trapped. There was no indication as to how many people might still be buried in the rubble.

"Everything at home kept falling down," Refik, a Tirana resident, told Reuters of the impact on his sixth-floor apartment.

"We were awake because of the previous quakes, but the last one shook us around," he told Reuters, referring to smaller tremors recorded in the hour before the main quake.

An unidentified man, with a wound dressing on his right cheek, told News24 TV his daughter and niece were among those trapped in a collapsed apartment building in Durres.

"I talked with my daughter and niece on the phone. They said they are well and are waiting for the rescue. Could not talk to my wife. There are other families, but I could not talk to them," the man said.

Local television stations showed footage of a young boy being pulled from a collapsed building in the coastal town of Durres, 33 kilometers (20 miles) west of the capital Tirana, after an excavator moved a broken slab of concrete and local men pulled mangled reinforcement bars out of the way.

Health Minister Ogerta Manastirliu said more than 600 people had been treated for injuries, including nine hospitalized with life-threatening injuries.

"It is a dramatic moment where we should preserve calm, stay alongside each other to cope with this shock,'' Prime Minister Edi Rama said.

The US Geological Survey said the Albanian quake, which struck just before 4 a.m. local time, had an epicenter 30 kilometers (19 miles) northwest of the capital, Tirana, at a depth of 20 kilometers (12 miles). Scores of aftershocks were recorded, included three with preliminary magnitudes of between 5.1 and 5.4.

The worst-hit areas were Durres, where nine of the dead were found in collapsed buildings, and the northern town of Thumane, where another five bodies were pulled from the rubble, the Defense Ministry said.

"Search and rescue work continues at all sites where buildings have collapsed,'' Defense Minister Olta Xhacka said in a televised statement. "But these are extremely difficult operations, where you have to work slowly because there is a high risk of further collapse, endangering not only residents, but also those trapped, and the rescuers themselves."

Seismologist Rrapo Ormeni of Albania's Institute of Geosciences, Energy, Water and Environment, said a 6.4 quake was considered a strong one.

"Damage at the epicenter will be considerable because of its high energy, the magnitude it has,'' Ormeni said. ``Such quakes are felt in a wider area due to its major depth and magnitude. It has been felt all around the territory of our country but also abroad, up to Bulgaria, Bosnia, Italy and other (countries).''

The quake was felt along the Albanian coast as well as neighboring Kosovo, Montenegro, Greece, and parts of southern Serbia.

Authorities called on people in the most affected areas to stay out of their homes and avoid driving in the affected areas to allow emergency vehicles free access. Many reported seeing cracks in their apartment walls.

International assistance

The United Nations says it is sending two technical experts from the U.N. Disaster Assessment and Coordination office to Albania following the earthquake that struck the country.

UN spokesman Stephane Dujarric told reporters that in addition to dispatching the technical experts to Albania, the UN is also ready if required to provide assistance to Bosnia, where minor damage was recorded from a separate, magnitude-5.4 quake Tuesday.

He said the UN is in contact with local authorities for more information on the situation.

The UN Disaster Assessment and Coordination office is designed to help the United Nations and governments of disaster-affected countries during the first phase of an earthquake, hurricane, severe flooding or other sudden emergency.

Foreign policy chief Federica Mogherini say the EU "is ready to offer assistance.''

The European Union's office in Tirana says Europe's civil protection mechanism has been mobilized to help in the aftermath of Albania's strong quake.

A statement from the EU delegation to Albania says Brussels has already helped mobilize 3 search and rescue teams to assist in ongoing search and rescue operations.

Teams from Italy, Greece and Romania are already in Albania, while Hungary, Germany, Croatia, France, Estonia, the Czech Republic and Turkey have also offered help.

Tuesday's statement said additional EU assets are on standby should they be needed.

Turkey's ambassador to Albania says a group of some 20 Turkish nationals were rescued from a hotel that was damaged in an earthquake that hit the country.

Ahmet Yoruk told CNN-Turk on Tuesday that Turks were staying in a hotel in the city of Durres, one the most affected areas from the magnitude-6.4 quake.

They were rescued with slight injuries and are being evacuated to Tirana, Yoruk said.

The ambassador also said Turkey is sending a team of rescuers and medics to assist Albania with the rescue efforts.

Albania located along the Adriatic and Ionian Seas, between Greece and Macedonia, Albania experiences regular seismic activity.

An 5.6 magnitude quake hit Albania on Sept. 21, damaging around 500 houses, Electricity and telephone lines were cut off in Tirana and a number of other towns and villages.

The images of damage from Tuesday's quake suggested it was stronger than one in 1979 which razed a district of a northern town. Neither of those two earlier quakes caused deaths.

The Balkan nation is the poorest country in Europe, with an average income of less than a third of the European Union average, according to Eurostat data.