Berisha says the death toll has risen to five and three of the bodies have been identified. He says 243 people have been registered as injured, and that 12 of them are in serious condition. The prime minister says the search and rescue operation has been halted for the night, and that it will resume early Sunday morning.
He says the destruction of ammunition at the dump was being carried out by an Albanian company that had been subcontracted by a U.S. company, and that there were no foreign citizens in the area at the time of the blast.
Four thousand people have been evacuated from three villages and the surrounding area, the prime minister says.
The initial blast at the depot at Gerdec village, about six miles north of the capital, Tirana, set off a series of explosions, and ammunition continued to detonate into the night. The blast was heard as far away as the Macedonian capital of Skopje, a distance of 120 miles, and prompted a brief suspension of flights at Tirana's nearby international airport, which was slightly damaged.
Houses more than a mile away were damaged by the blast.
Footage from Albanian television showed a massive ball of fire shooting up from the site, while shrapnel and shell fragments rained down on homes and vehicles.
The continuing explosions were hampering rescue efforts, and authorities were unable to get to the site of the main blast to assess how many casualties there were. The blast also damaged a major electricity transmission point, leaving the area without power and creating further difficulties for rescuers, authorities said.
"The most dangerous area, where it is foreseen there will be dead, is the explosion site where none has been able to go yet," said Interior Minister Bujar Nishani. He said authorities evacuated the surrounding area and explosives experts would clear the area of remaining ammunition in the next few days.
Police said the cause of the explosion was not immediately clear, but terrorism was not suspected.
Health Minister Nard Ndoka said many of the injured were children, and that 12 of the injured were in serious condition.
Prime Minister Berisha, a cardiologist, visited victims in hospitals in Tirana and said most of the injured were suffering from burns and psychological shock.
The health minister said Albania had received offers of assistance from Italy, Greece, Switzerland and many other countries to treat the injured.
Italy was sending a plane carrying medical personnel and equipment in response to an Albanian request. France and the United States have offered help and support.
In neighboring Kosovo, where most of the population is ethnic Albanian, hundreds of people lined up at a Pristina hospital to give blood, and NATO-led peacekeepers were sending blood reserves by helicopters, officials said.
In Skopje, Macedonians donated blood; Macedonian Foreign Minister Antonio Milososki was heading to Tirana to offer assistance, and donating blood himself.
Greek Foreign Minister Dora Bakoyannis said she has expressed Greece's solidarity and intention to help.
Berisha's office issued a statement quoting witnesses as saying that 110 people had been working at the dump at the time of the explosion. It said they reported that there had been a delay of about 10 minutes between the initial blast and the explosions that followed, and that many of the workers had managed to run away.
The army depot is used as a location to destroy excess ammunition.
Albania has some 100,000 tons of excess ammunition stored in former army depots across the country, according to Defense Minister Fatmir Mediu.
NATO countries, and particularly the United States, Canada and Norway, have been helping with funding for Albania to destroy excess ammunition and obsolete weaponry.
"The problem of ammunition in Albania is one of the gravest, and a continuous threat," Berisha said. "There is a colossal, a crazy amount of them since 1945 until now."
He said he did not exclude human error in Saturday's blast, but added that the ammunition could have exploded spontaneously because of its age.
Albin Mecaj, 22, who works at the depot, told The Associated Press by telephone that about 80 people had been working on destroying ammunition at the time of the explosion. Mecaj, who was badly burned in the blast, said about 120 people usually work at the depot.