Brisbane woman missing since UK attacks

There are fears for a young Brisbane woman who was last seen on London Bridge before the weekend's terror attacks.

Family and friends of Sara Zelanak, 21, have taken to social media to appeal for information about the missing Australian who hasn't been heard from since the attacks on Sunday morning (AEST).

A Facebook post written by a friend, which has since been deleted, said Ms Zelenak was last seen on London Bridge and witnessed the terror attacks before getting separated from her friends.

"Her phone has rang with no reply and now the battery must have gone," read the post, which has been shared numerous times.

"She is Australian aged 21 with long blonde hair. She calls her mum daily. It's been over 24 hours with no news from the consulate. We was hoping the 3rd Australian reported would be her, but it's not.

"She is based in London. Please share with as many people as possible especially if you have friends down south. Thank you for your help."