In addition to Brisbane woman Candice Hedge and Darwin man Andrew Morrison - both injured in stabbing attacks - the government now has "very real concerns" about two other Australians who have not been identified.

However, he would not say whether the two others were unaccounted for, saying authorities were "in close touch" with the Australians' families, and it would not be appropriate to say any more at this stage.

At least seven people were killed and 48 injured in the weekend incident, which targeted the area surrounding Borough Market and London Bridge in the centre of the city. Three suspected terrorists were killed and a dozen arrests have been made.

Mr Turnbull said one of the Australians was in hospital and another was returning to Australia.

"There are two other Australians, so that brings it to a total of four, about whom we have very real concerns. But at this stage, we're not able to say anything more," Mr Turnbull said.

"We have been in touch with their families, in close touch with their families, as we seek to find confirmation of the circumstances of the two other Australians."

Earlier on Monday morning, Foreign Minister Julie Bishop had confirmed three Australians had been affected.

Ms Hedge, 34, has been left unable to speak after being stabbed in the throat.

"She can't talk. She's been stabbed around her neck, her throat. She's all bandaged up." her mother, Kim Del Toro, told Fairfax Media.

"She went into surgery, but she's going to be fine, thank goodness."

In a video posted to social media website Reddit, Mr Morrison, an electrician, said: "He got me but I dodged it, I ducked and weaved."

Mr Morrison's sister Katrina, said he was safe and a flight home was being arranged.

"Yes my brother was involved," she said. "We're currently sorting out his flight home ... Yeah, right now we are just happy he is safe," she said.

Ms Bishop said Australia's responses to the "ever-changing threat" of terror incidents were constantly under review.

"The mindless savagery that we've seen in London is designed to shock people and to divide communities and so we must be resolute in our determination to defeat terrorism and defeat the ideology that inspires so many people," she said.

"And the voices of moderate Islam must be louder than the voices of radicalisation and savagery and brutality."

Prime Minister Malcolm Turnbull, who met with national security advisers and cabinet colleagues on Sunday after the attack, said Australia stood in "resolute solidarity" with the people of Britain.

"This attack is yet another cruel example of the new reality with which we live, the ever-present threat of murderous Islamist terrorists, intent to harm our communities, our way of life and the freedoms we hold dear."

One Nation leader Pauline Hanson came under fire after she co-opted a London police warning to make a point about Islam, even as the crisis was still underway.

Senator Hanson paired the "Run Hide Tell" slogan - used by police to inform people how to respond to the threat as the attack unfolded - with a series of social media posts calling for an end to Muslim migration.

"Stop Islamic immigration before Australia hits the 5 per cent like England," she said.

Opposition Leader Bill Shorten called her comments "crass, idiotic and disgusting".

Ms Bishop said it was "too simplistic to try and narrow it down to one cause".

"We have to remember that these attacks are being undertaken by people from every different walks of life," she told ABC radio.

"Some are British-born or homegrown, as they say. Some are lone wolf attacks. Some of them are people who have no previous links with ... Islam. Some of them are obviously at the direction of ISIS. Some are merely inspired. Some could be copycat."

with Steve Lillebuen, Rachel Browne, Lynette Eyb