De Almeida said 18 others were injured at around noon (11:00 GMT), four and a half hours before the pope was due to speak, when the gates of the stadium opened.
The two died at the scene. Eight others were taken to the Josina Machel hospital with injuries, he said.
But Maria das Dores Celina, a nurse at the Josina Machel Hospital in downtown Luanda, told the Reuters news agency that two girls, in their teens, arrived dead at the hospital on Saturday.
"Their bodies were bruised. They were probably trampled as they rushed inside the stadium."
One of the eight injured, a 27-year old woman, was crushed in the frenzy and collapsed shortly after entering the stadium.
Police officials said over 30,000 people, including mothers with babies, attended the rally in sweltering heat.
|The pope will perform an open-air mass on Sunday to about half a million people [AFP]
"There were just too many people inside the stadium and the temperatures were too high," Conceicao Cassange, 27, said as she lay on a hospital bed. "I think tomorrow things could be worse."
De Almeida said a police investigation had been launched into the incident.
On Sunday, the Pope will perform an open-air mass for half a million people. He is in Angola on the second and last leg of a tour of Africa, his first visit to the continent since taking over as pontiff. He will return to Rome on Monday morning.
Over 60 per cent of Angolans are believed to be Catholic - a religion introduced by Portuguese missionaries 500 years ago.
More than half of Angola's population is under 18, and many bear physical scars of the decades of fighting that has left the southern African country one of the most heavily landmined nations on the planet.