A hostage who died in the Sydney siege has been lauded as a hero following reports that she was killed as she was shielding her pregnant friend from gun shots.

Katrina Dawson, a female barrister, was shot and killed during a siege by lone wolf attacker Sheikh Man Monis. Police have not confirmed if she was killed by stray gunfire or by Monis himself.

Dawson was having a cup of coffee with one of her colleagues at the Lindt cafe when Monis entered the shop and took 17 staff and customers hostage.

Tori Johnson, 34, the manager of the Lindt Chocolat Café in Martin Place was also killed alongside Dawson in the final stages of the 16-hour ordeal, when he allegedly attempted to snatch the attacker's shotgun.

At a prayer service in the Australian city, Archbishop Anthony Fisher praised both Dawson and Johnson of their heroism and spoke of the heartbreak caused "by the deaths of two innocents".

"Reports have emerged this morning of the heroism of the male victim of this siege," Archbishop Fisher said.

"Apparently seeing an opportunity Tori Johnson grabbed the gun - tragically it went off killing him.

"But it triggered the response of the police and eventual freedom for most of the hostages.

"Reports have also emerged that Katrina Dawson was shielding her pregnant friend from gunfire. These heroes were willing to lay down their lives so others might live."

Deputy Police Commissioner Catherine Burn could not confirm reports of either hostage's heroism, saying that investigators were still piecing together events of the siege and its conclusion.

Monis, an Iranian native known to police for a series of alleged offences, including being accessory to the murder of his wife, burst into the Lindt Cafe on Monday morning and took 17 people hostage.