Ms Bishop said she was deeply saddened to announce the deaths of two young Australian women, after they were both "attacked savagely" in London on Saturday night, local time.

Ms Bishop said government officials were working with British authorities to confirm the identities of the victims, before formally releasing their names.

The family of South Australian nurse Kirsty Boden has already paid tribute to the 28-year-old, saying she was running to help victims of the stabbing and van attack on London Bridge and Borough Market when she was killed.

Another Australian - 21-year-old Sara Zelenak from Brisbane - had been reported missing in London, after she was last seen running from the three attackers. On Tuesday, Ms Zelenak's family said they had been bracing themselves for the worst.

On Wednesday morning, Ms Bishop said the families of the two Australian victims were on their way to London.

She said she could not publicly identify the victims, at the request of British authorities. That confirmation was expected later on Wednesday.

"The families have asked for privacy. You can understand what a harrowing time they're going through. [They were] two beautiful women enjoying a night out in London and, I have to say, the savagery of these attacks is just beyond belief," Ms Bishop told radio station 2GB.

"The British authorities are being meticulous and methodical in the identification, the coronial processes and the notification processes. There are a number of foreigners involved and foreign governments ... This has meant official notification has been somewhat slower than you might expect.

"It's just such a tragedy and, of course, coming on top of what we've seen in Melbourne, it really does make us reassess once more to ensure that we have got the processes, the procedures in place to keep Australians as safe as possible."

The two Australian women were among seven people who died in the London attack, before the three terrorists were shot dead by police. A further 48 people were injured in what was Britain's third Islamist attack in as many months.

The three attackers, who were wearing fake explosive belts, have been named as Khuram Butt, 27, Rachid Redouane, 30, and Youssef Zaghba, 22.

Just after 10pm on Saturday, the men rammed a van into pedestrians on London Bridge before running into the Borough Market area, where they slit throats and stabbed people indiscriminately.

Ms Boden worked for Guy's Hospital in central London, about 300 metres away from London Bridge, as a staff nurse in theatre recovery. Her family said she was trying to help people on London Bridge when she died.

Ms Boden was "loved and adored by her family, friends and boyfriend", her family said in a statement.

"She was the most outgoing, kind and generous person who loved to help people," they said.

"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."

Ms Zelenak, who was working as an au pair in London, had just finished dinner with her friend, Pri Gon??alves, near London Bridge on Saturday night when the van crashed into pedestrians on the bridge.

The pair became separated as people began running from the attackers, Ms Gon??alves said.

"Sara was with me when people started running and shouting but at that very moment we got separated," she said.

Ms Zelenak was wearing high heels and Ms Gon??alves fears that may have caused their separation.

"I ran, thinking she would be running with me but I looked back and she wasn't there," she said.

Ms Zelenak's parents, Julie and David Wallace, were planning to head to London to search for their daughter as soon as possible.

Mrs Wallace told Brisbane radio station 97.3FM this week of her "absolute terror" when she received a phone call from her daughter's host family in London.

"The mother rang to say that she gave her the night off so she could go out with her friends and she was heading for the London Bridge where everyone goes on a Saturday night and all the action is," she said.

"And that was at night, I thought 'They're just expecting her to walk in the door any time,' and she never came back."