* Magnitude 6.4 quake strikes near Tirana
* "Roof collapsed on our head" - survivor
* 45 pulled alive from rubble
* Second tremor to hit Balkan region in two months
* Firefighters, army staff join rescue effort
* GRAPHIC - https://tmsnrt.rs/2KUWRQo (Updates injury figure, aftershocks)
TIRANA/DURRES, Albania, Nov 26 (Reuters) - At least 21 people were killed when the most powerful earthquake to strike Albania in decades shook the capital Tirana and the country's west and north on Tuesday, tearing down buildings and burying residents under rubble.
Residents, some carrying babies, fled apartment buildings in Tirana and the western port of Durres after the 6.4 magnitude quake struck shortly before 4 a.m. (0300 GMT).
The Balkan country was jolted by 250 aftershocks after the main tremor, Defence Minister Olta Xhacka said, two of them of magnitude 5, testing strained nerves.
She told reporters that the quake's epicentre was in Durres, Albania's main port and a tourist spot, adding: "Around 600 residents were injured and received treatment."
In the northern town of Thumane, Marjana Gjoka, 48, was sleeping in her apartment on the fourth floor of a five-storey building when the quake shattered the top of the building.
"The roof collapsed on our head and I don't know how we escaped. God helped us," said Gjoka, whose three-year-old niece was among four people in the apartment when the quake struck.
The quake was centred 30 km (19 miles) west of Tirana, the U.S. Geological Survey (USGS) said, and was also felt across the Balkans and in the southern Italian region of Puglia, across the Adriatic Sea from Albania.
Hours later a magnitude 5.4 earthquake rattled Bosnia, with an epicentre 75 km (45 miles) south of the capital Sarajevo, monitors said. There were no reports of injuries.
In Durres, 13 bodies were pulled from collapsed buildings and 45 people were rescued from the wreckage there and in Thumane.
After a 14-hour ordeal, a 30-year-old woman was extracted alive from the ruins of a six-storey building, two hours after police removed the body of her eight-year-old daughter.
At dusk, a woman called Bukuri Morina and her family of 10 joined thousands of others to spend the night at the Durres soccer stadium, where the army had pitched tents.
"We are afraid to go back to our apartment," she said. "There are cracks all over and we are afraid that we will have the same destiny as people in Thumane."
Located along the Adriatic and Ionian seas, between Greece and Macedonia, Albania experiences regular seismic activity.
A 5.6 magnitude quake hit Albania on Sept. 21, damaging about 500 houses. The Defence Ministry said then it was the most powerful quake in Albania for the past 30 years.
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.
Albania is the poorest country in Europe, with per capita income a quarter of the European Union average, according to the International Monetary Fund.
For a graphic on the location and intensity of the quakes, click - https://tmsnrt.rs/2KUWRQo
"EVERYTHING KEPT FALLING"
In Thumane, seven people, including a mother and son, were found dead in the brick rubble of two apartment buildings and a man died in the town of Kurbin after jumping out of a building.
Firefighters, police and civilians were removing the debris from collapsed buildings in Thumane. Some used a mechanical digger to claw at collapsed masonry and remove a tangle of metal and cables. Others scrabbled with their bare hands.
Two people were pulled from rubble in Thumane four hours after the quake, a Reuters reporter said. Doctors said they were in a bad condition.
"Everything at home kept falling down," Refik, a Tirana resident, said 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.
Rescuers told local media one of the dead was an elderly woman who saved her grandson by cradling him with her body.
"Durres and Thumane are the areas worst hit. Rescue-and-save work continues in the collapsed buildings there," Xhacka, the defence minister said, as troops extricated a victim from a stricken hotel in Durres.
Italy, France, Romania, Turkey, Greece, Croatia, Montenegro, Kosovo and Serbia sent 200 specialised troops, tools and teams of tracker dogs to help the relief effort, Xhacka said.
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.
(Reporting by Benet Koleka in Tirana and Fatos Bytyci in Thumane and Durres, with additional reporting by Lefteris Papadimas and Suzana Sabljic Writing by William Maclean Editing by Mark Heinrich)