Seven people have now been murdered in stabbings and shootings in the capital since last Wednesday.
A man, believed to be in his 40s, was found with stab wounds Walthamstow, east London, at 9.50pm on Monday.
Paramedics battled to save him for over an hour but he was pronounced dead at the scene in Vallentin Road, near Wood Street Tube station, at 10.55pm.
Scotland Yard said officers are in the process of informing his next of kin and a post mortem examination will be held in due course.
A woman aged 36 was arrested two hours later on suspicion of murder. She remains in police custody.
A second man died after turning up at a west London hospital with stab injuries.
Police say the victim, whose age is not known, is believed to have been attacked during an “incident” in Marlborough Road, Southall.
He was declared dead in hospital at 6.14pm.
It comes after Scotland Yard launched five murder investigations in as many days across the capital last week, in Hackney, Houslow, Enfield, Chadwell Heath and Walthamstow.
Meanwhile, two 20 year old men were shot in Nash Road, Chadwell Heath, on Monday night - the same road an 18-year-old man was stabbed to death in last Wednesday.
They were taken to hospital with non-life threatening injuries after the incident at about 11.30pm, the Met Police said.
And two boys were rushed to hospital last night with after being stabbed in Streatham, south London. Neither suffered life-threatening injuries.
Emergency services had been called to Hopton Road at 7.50pm.
No other arrests have been made following Monday's incidents, police said.
