A man reportedly tried to enter government offices in Sydney's CBD yesterday demanding to see the Attorney-General, 7News has reported.

The same man is believed to be involved in a siege inside the barrister's chamber in Parramatta today.

At 6pm the situation was described as "tense and delicate" as negotiators and police spoke with the man who entered the offices at 9am this morning claiming to have a bomb in his backpack.

According to an interview with the office manager at the scene earlier today, a man came into office looking for a man the office manager didn't know.

The man is said to have "snapped" at the reply and claimed he had a bomb in his backpack.

In an interview with the ABC the office manager said, "When I told him there was no-one here by the name he then went to the front of the building and said, 'Call the Attorney-General's department, call this person, and tell them I've got a bomb in my backpack'."

It has been reported that a young girl accompanied him and referred to him as "dad".

7News later reported that the girl is now believed to be in her early teens and the man is in his 50s.

Earlier a man appeared at the window, pulling back a blind and holding a barrister's wig up to the window, while making a thumbs-down gesture.

He was seen pointing at himself and giving the thumbs-up, then pointing to the wig and giving the thumbs down.

Police addressed the media about the hostage emergency in Parramatta this afternoon saying they remain concerned about the safety of the young girl.

Contact with the young girl has been made, reports say. Police say she is in as good of a condition as can be expected.

NSW police told the media the man has been talking to negotiators over the day.

Police are still concerned about the backpack and say until they have possession of the backpack we will remain concerned.

Armed police entered the building at 2pm this afternoon.

They have closed off George Street from O'Connell and Marsden Streets

This morning, an ambulance spokeswoman said four crews had been sent to the courthouse.

"We are attending an incident at Parramatta," she told AAP.

ABC Radio reported that a courts spokesperson confirmed a "hostage situation" in Parramatta this morning.

EYEWITNESS ACCOUNT

Jessica Hanna, who works a few doors down from the scene at the Nyman Gibson Stewart law firm, told AAP police had cordoned off her office but she had not been advised to leave.

"They've wrapped (our office) all up ... I'm concerned," she told AAP.

Ms Hanna said police were on the scene from around 9am (AEST) on Tuesday.

"When I arrived this morning ... I saw police rock up on the corner of the local court, park their car, run across the opposite side of Marsden Street ... and then they ran back," she said.

"As I was coming to work there was a cop (who) rocked up as everyone was waiting there to see what was going on.

"I noticed a few people had been evacuated out of the building.

"All I know was what I've heard from police. I've asked him, and (he said) I think it's okay at this stage."

Ms Hanna said she believes the incident occurred in a law office.

Police have ruled out reports that the man who entered the building was armed with a collar bomb.

"At this stage it is not known what caused the man to attend the building or what he is in possession of," a spokeswoman told AAP.

More to come