UPDATED: The Federal Government has officially confirmed that two Australians were killed in the London terrorist attack.

UK police on Tuesday night confirmed Australian nurse Kirsty Boden was killed in the attack, which began on London Bridge and swept through nearby Borough Market.

Meanwhile, there have been grave fears held for 21-year-old Brisbane woman Sara Zelenak, who has not been heard from since she was last seen on London Bridge in the midst of the attack.

Ms Boden, 28, lost her life after running toward the carnage on London Bridge to help victims of the terror rampage that killed seven people and left 48 injured.

The Australian government on Wednesday morning said British authorities had asked Australia to hold off on releasing the name of the second victim pending official confirmation and the family being officially notified.

“The Australian Government is deeply saddened to confirm that two Australians have been killed in the London terrorist attack,” Foreign Minister Julie Bishop said in a statement.

“The Australian Government has remained in close contact with the families who have requested privacy.

“We ask the media to respect their request at this difficult and harrowing time.”

The family of Ms Zelenak earlier said it was “bracing for the worst” as it awaited news of what happened to her.

Ms Zelenak became separated from friends during the attack. Her family and friends have not heard from her since and she was known to phone her mother daily.

Ms Zelenak’s mother, Julie Wallace, is travelling to the UK in an attempt to find her.

Prime Minister Malcolm Turnbull says he has contacted the families of two Australians victims. 

The Prime Minister confirmed he has spoken with the family of Ms Zelenak.

“I am a father … Kirsty or Sara could be one of my kids, it could be one of your kids,” he told 3AW’s Neil Mitchell on Wednesday.

“This is heart-rending, this is the last thing anybody expects to happen to their children when they are in London.”

The government’s confirmation comes as police named the third of the terrorists who killed seven people in the knife and van attack as an Italian national of Moroccan decent.

Italian media report Youssef Zaghba, 22, had been flagged to Britain as a possible militant by Italian authorities.

Ms Boden had lived and worked in London as a nurse for some time.

In a statement issued by police on behalf of her family, the 28-year-old was described as being “loved and adored by her family, friends and boyfriend”.

“She was the most outgoing, kind and generous person who loved to help people,” the statement read.

South Australian Kirsty Boden died in the London terror attack.

“Helping people was what she loved to do in her job as a nurse and in her daily life.

“As she ran towards danger, in an effort to help people on the bridge, Kirsty sadly lost her life.

“We are so proud of Kirsty’s brave actions which demonstrate how selfless, caring and heroic she was, not only on that night, but throughout all of her life.

“Kirsty – we love you and we will miss you dearly.”

The Boden family has said it will not be making any further comments on the tragedy and have asked the media and the public to respect their privacy to grieve away from the public eye.

Grave concerns for missing Australian Sara Zelenak

Missing Sara Zelenak was given the night off work on the evening of the London terror attack. Photo: AAP

Ms Wallace said her daughter, Sara Zelenak, had been given the night off working as an au pair to go out with a friend.

“She was heading for the London Bridge where everyone goes on a Saturday night,” Ms Wallace told Brisbane’s 4KQ radio station.

It was Ms Zelenak’s host family who called the family back in Australia to tell them she had not come home.

Ms Zelenak’s friend Pri Goncalves says they became separated on the bridge when the attacks started.

“Sara was with me when people started running and shouting but at that very moment we got separated,” she told Fairfax Media.

Ms Goncalves says she has been desperately trying to contact her friend since they were separated.

“When I was close to Borough Market I saw a guy on top of another guy who was screaming and then I knew something really bad was happening. I think he was stabbing him,” she said.

“So I started calling her (Sara) but she never picked up the phone.”

Third attacker named

All three London Bridge attackers have now been identified.

British police said Zaghba had not been a subject of interest for them or the MI5 domestic intelligence agency.

Earlier, Italian newspaper Corriere della Sera reported that Zaghba had been stopped at an Italian airport because authorities believed he was on his way to Syria, and that Italian officials had warned British counterparts about him.

Police previously named the other two attackers as 27-year-old Khuram Butt, a British national born in Pakistan, and 30-year-old Rachid Redouane, who had claimed to be Moroccan and Libyan.

Butt was previously known to security agencies and had appeared in a British TV documentary called The Jihadis Next Door.

All three of the London Bridge attackers were shot dead at the scene by officers within eight minutes of police receiving the first emergency call.

A nationwide minute of silence was held at 1000 GMT to honour all the victims.

London attackers Khuram Shazad Butt, (left), Rachid Redouane (centre) and Youssef Zaghba (right). Photo: AP

Two other Australians were caught up in the attack: Candice Hedge of Brisbane and Andrew Morrison of Darwin.

Both received stab wounds to the neck, with Ms Hedge requiring surgery and Mr Morrison requiring stitches.

Seven people are confirmed dead after the attack, which also left 48 people in hospital.

The attack began shortly after 10:00pm (London time), when a van carrying three men struck pedestrians walking across London Bridge.

The attackers then began stabbing people throughout the Borough Market area before they were shot dead by police.

 – with AAP/ABC