Updated 2.55pm: The world will be watching as an inquest into the Lindt cafe siege opens in Sydney today.

A large international media contingent, including the BBC, CNN and The New York Times, is expected to attend the opening day as the inquest tries to determine how gunman Man Haron Monis and two hostages, Katrina Dawson and Tori Johnson, died.

Only one hostages of Sydney's Martin Place siege has turned up to today's inquest - which is now underway at a coroner's court in Australia.

82-year-old John O'Brien is watching on - along with the family of victim Tori Johnson - but no members of Katrina Dawson's family are there.

The inquiry will look into what happened inside the Lindt cafe, how it was dealt with and whether the deaths of the gunmen and the two victims could've been prevented.

Barrister Jeremy Gormly says they'll also look into what contact hostages had with the outside.

"What interactions occured between police, hostages, non-police parties and hostage families. How did social media contact impact the prospect of resolution."

The inquest has confirmed victim Katrina Dawson was killed by a stray bullet.

Barrister Jeremy Gormly's detailed exactly how it happened to the coroner's court.

"Ms Dawson was struck by six fragments of a police bullet or bullets, which ricochet from hard surfaces into her body. One struck a major artery, she lost consciousness and died soon afterwards."

No witnesses will be called, but counsel assisting will outline the scope of the inquest and the results of inquiries to date.

The inquest is expected to adjourn until later in the year.