Hostage-takers have freed 32 women and infants from a school in south Russia, but they are still holding more than 300 people, among them many children.
Very young children were among those released
Officials said they were working to maintain contact with the attackers, with the crisis well into a second day.
Authorities ruled out using force to end the siege in North Ossetia, and Russian President Vladimir Putin said the hostages' safety was paramount.
Desperate parents are maintaining a vigil outside the school in Beslan.
Late on Thursday afternoon, women cradling very small children emerged from the building and were whisked away in cars by security forces, as the crowd rushed forward to find out who had been freed.
Officials said the breakthrough came after mediation efforts by the former president of the neighbouring region of Ingushetia and that negotiations would continue.
As the siege continued, anger and frustration was growing among the families.
Some of the hostages have reportedly been able to phone home, describing conditions in the school as tolerable.
Inside are pupils, teachers and parents who had come to the school on Wednesday morning to help celebrate the first day of term.
"Our main task is to save the life and health of those who have ended up as hostages," said President Putin who cancelled a working holiday and visit to Turkey to deal with the crisis.
The head of the Russian security service in North Ossetia has said there is "no question" of opting for force at the moment.
"There will be a lengthy and tense process of negotiation,"
Valery Andreyev was quoted as saying by Reuters news agency.
North Ossetia's Interior Minister Kazbek Dzantiyev said 12 civilians had been killed since the siege began, Itar-Tass reports.
The hostage-takers began talking overnight to prominent paediatrician Lev Roshal, who helped negotiate the release of children during the siege of a Moscow theatre in 2002.
Mr Roshal said they refused offers to deliver food and water, but he was assured the children were fine.
Masked men and women, wearing bomb belts, burst into the school, whose pupils are aged seven to 18, at around 0930 local time (0530 GMT) on Wednesday.
The hostages were herded into the gym. Up to 50 children were reported to have escaped in the confusion.
RECENT DEADLY ATTACKS
31 Aug 2004 - Suicide bomb kills 10 at north Moscow train station
24 Aug 2004 - Two planes crash after leaving same Moscow airport, killing 89
May 2004 - Chechen president killed in blast at stadium in Grozny
Feb 2004 - Bomb attack kills at least 39 people on Moscow underground
Dec 2003 - Female suicide bomber kills five near Red Square
Trip wires are believed to have been laid around the school, with the attackers threatening to blow it up if stormed by police.
Mr Dzantiyev was quoted as saying on Wednesday they threatened to kill 50 children for every fighter killed.
The hostage-takers' exact demands are unclear, but they are said to be calling for the withdrawal of Russian troops from Chechnya and the release of Chechen rebels held in Ingushetia.
The Russian authorities are blaming what they call international terrorism, with suspicion falling on Chechen separatists, who have been fighting for independence from Moscow for the past decade.
Chechen rebel leader Aslan Maskhadov has denied that his forces are involved in the siege.
The school crisis came a day after a suspected suicide bombing in Moscow killed 10 people. Last week, the mid-air explosions of two passenger planes left 89 dead.
1 - Main entrance
2 - Area where gunfire began
3 - Hostages are being held in the school gym, which has reportedly been packed with explosives and mines
4 - Side entrance
5 - There have been reports of children being used as human shields at the back windows
6 - As the attack began a number of people hid in the boiler room and later escaped