The unnamed 29-year old suffered multiple, severe stab wounds to her head and body in what police described as an "extremely brutal" attack.
She was attacked yards from her home after getting off a bus in Krithia Road, Dagenham, at 21:40 GMT on Monday.
Police say they believe the attack was carried out by a stranger but are "keeping an open mind".
Passers-by attempted to help the woman, who remains in a critical condition in a hospital in east London.
Due to the nature of the attack investigators do not have a description of a suspect at this point and there have been no arrests.
Police appealed for two women who stopped to help the victim, or anyone else with information, to contact them.
DCI Gary Holmes, of Homicide and Major Crime Command, told BBC London: "This is a really brutal and horrific stabbing of a young lady coming home from work.
"That attack has left her in a terribly critical condition, currently in hospital in a life threatening condition and we are desperate to locate the person who committed... that attack."

The city's mayor said test results had showed no contamination, and locals could resume using water for drinking, bathing and cooking.
The ban was issued on Wednesday over fears that a leak at an asphalt plant could have tainted the water supply.
Long queues formed at grocery stores as shoppers stocked up on bottled water.
About 85% of Corpus Christi, which has a population of about 320,000, was under the restrictions.
The chemical behind the scare was Indulin AA-86, an asphalt emulsifier which can burn human skin in its concentrated form.
The leak took place at an asphalt plant leased to Ergon Asphalt and Emulsions by oil refiner Valero.
Mayor Dan McQueen told a news conference that investigations into the 24-gallon (91-litre) spill of Indulin AA-86 had determined that the water was safe to use.
It was not clear if the public water supply was ever contaminated by the chemical.
Officials said that none of the 28 drinking water samples analysed by the Environmental Protection Agency (EPA) tested positive for the contaminant.
However, the EPA said there have been seven "unconfirmed" reports of symptoms possibly related to prohibited water use.
Mr McQueen said officials would seek possible damages from those responsible for the leak.
There has been some confusion over exactly when city officials were notified of the problems at the plant that prompted the water use ban.
Valero Energy Corp said in a statement on Saturday that it had alerted the city to "milky, sudsy water" at the plant on 7 December - a full week before the ban was announced.
Ergon said the issue arose when "soap solution" flowed back into a pipe through which the plant receives water.
It said the pipe is not directly connected to the city's water main, but that the two are interconnected.
Corpus Christi locals have been warned to use water conservatively to avoid overtaxing the system.
The EPA will continue collecting and testing water samples in the city over the coming days.
A woman in east London has been left fighting for her life after an apparently random knife attack.
[NEXT_CONCEPT]
Residents of Corpus Christi, Texas, have been told it is safe to drink tap water again, after a chemical leak sparked a four-day ban.