Emma was heading to a friend's house to watch a movie late on Saturday 19 September. Victoria Police say the attack happened about 11pm on Sunshine Road, and that the Wantirna South rider, 27, was hospitalised with serious injuries that were not life-threatening.

"This was not a risk I ever thought or imagined," Emma said during an emotional press conference.

Before she was cornered, the riders had motioned towards her further back along the road. She ignored them, thinking "they were just being silly." When they drew alongside again, "very erratic," she sped up to get clear.

She stopped at a red arrow behind a car already at the lights. "Then, very, very quickly, I had one motorbike pull up next to me and another one cut me off," she said. She sensed more people behind her. Police say some offenders circled her on their bikes during the attack.

"I felt every taser... every time they hit my head," she said.

Police say she was punched and kicked repeatedly, tasered and struck with a baton. "It did not feel like just a fist. It felt like there was some weapon in their hand," she said. "I could feel it against my helmet."

The longer she held on, the harder the blows came. She let go, she said, because "my helmet was not gonna continue to protect my head forever."

The blows did not stop once the gang had the motorcycle. After letting go, Emma heard one of the men remark on her being a woman. She cannot recall the exact words, but said it was "something along the lines of, let's get her." She believes that moment is in the published footage, which shows the attackers still striking her head after taking the motorbike. Police have released CCTV showing four riders who detectives believe can assist them.

She does not think the attack began because of her sex, as her gear is bulky, but she heard the men call her "she" or "her" and keep hitting her.

"I think they were frustrated that, because I was a female, I would seemingly be weaker," she said. "I believe they took it personally, that they, as a group, could not remove one female" from the bike.

"The fact that it was one female versus multiple males, assumed males... in my mind, does make it a lot worse," she said.

The gang then rode away, and so did the motorists around her. "People started driving off straight away," she said. "I was just scared I would be left there by myself with no phone, no motorbike."

The car in front pulled away on the green light and nobody got out to help. The occupants of the car behind her, "very lovely, and in shock themselves," assisted once she walked over.

A woman beaten at a traffic light in view of motorists, by men who kept swinging after they had the bike, is a sign that violent gangs in Melbourne's west are not being deterred. Victoria Police figures released last week show carjackings and attempted carjackings down 25.4 per cent in the year to June, yet the force acknowledged that "crime levels remain unacceptably high" while carrying 1340 full-time equivalent vacancies for sworn officers.

Emma suffered a fractured rib, taser burns in several places, bruising, a bruised ear and swelling to her head. "I am incredibly lucky," she said. Since the attack she has had moments of crying, or of fright when "something flashes in the corner of my eye."

"It will probably be the worst moment of my entire life," she said.

"They're cowards... cowardly, disgusting, violent," she said. "I'm not expecting to get my motorbike back, but they need to be caught."

Detectives from the Westgate Divisional Response Unit believe the same gang struck twice earlier that Saturday. About 12.20am, a 40-year-old rider stopped on Napier Street was hemmed in, assaulted and robbed of his motorbike, which was found burnt out about an hour later at Presidents Park in Wyndham Vale. Ten minutes on, a 32-year-old on a scooter on Sunshine Road was surrounded, hit with a wrench and beaten as the riders demanded his keys.

Police have described the offenders only as "a group of six male offenders, who were all riding motorcycles." No arrests have been announced, and Emma's motorcycle is still missing.

Detectives want motorists who were nearby at the time to check their dashcam recordings. Anyone with footage or information should call Crime Stoppers on 1800 333 000 or lodge an anonymous report at www.crimestoppersvic.com.au. The investigation is continuing.