A phone call made by a hostage killed in the Sydney siege to the emergency services has been played at an inquest.

As well as audio of the call made by hostage and Lindt Cafe manager Tori Johnson, who was killed by gunman Man Haron Monis, the inquest was shown CCTV footage of Monis approaching the cafe on the morning of the siege in December 2014.

Monis forced Mr Johnson to ring emergency services and at gunpoint made him read out demands from a handwritten note that was found at the scene after the siege ended.

"This is a message that I'm reading from someone who's standing in front of me," Mr Johnson begins by saying.

The emergency services phone operator then replies: "Right, so there's an object is there?".

"There's bombs in three locations," Mr Johnson replies.

Mr Johnson then started reading from the handwritten note Monis had drafted.

"Australia is under attack by Islamic State. There are three bombs in three different locations - Martin Place, Circular Quay and George Street".

"I want to contact other brothers and ask them not to explode the other two bombs but I can't contact because they don't carry a phone with them. They have radios with them".

"I can say that through radio ABC (Australian Broadcasting Corporation)".

"The plan is to request Tony Abbott (Australian Prime Minster at the time) to call them or me and to have a debate while it is broadcast live on ABC national radio".

Lawyers for Mr Johnson's family had asked for the call not to be played out of sensitivity to the family, but the coroner ruled the public interest outweighed that consideration.

Mr Johnson was one of two hostages who died in the 17-hour siege.

The other, lawyer Katrina Dawson, was killed by fragments of police bullets, while 50-year-old Monis was also killed.

The latest phase of the inquest at New South Wales Coroner's court is expected to last for several weeks, and the coroner is expected to hand down his findings later this year.