A 26-year-old man was attacked with a knife in Colindale, north London, just before 6pm on Sunday and a woman in her 30s was stabbed to death in Brixton, south London, shortly after 6.30pm.
Officers, paramedics and London's Air Ambulance rushed to Chestnut Ave at about 10.50pm, but the man was pronounced dead at the scene.
A man in his 20s has been arrested on suspicion of murder over another killing in Brixton.More news: Saturday's Outlook: What To Expect From The Severe Weather Threat
A 34-year-old woman, known to the victim, has been arrested on suspicion of murder.
More than 35 people have been stabbed to death in the capital so far in 2018.
At a house in Brixton a woman in her 30s was killed and...More news: 'Where's the legal basis?' Corbyn challenges legality of Syria missile strikes
Eighteen-year-old Israel Ogunsola was stabbed to death in Hackney just days later. When they arrived to the scene, they found the victim, Christopher Miles, dead.
So far no one has been arrested in connection with the stabbing. I am in close contact with the police and I am reassured that they are doing everything they can to bring those responsible to justice and keep Londoners safe.
He was taken into custody at a north London police station.More news: Trump strikes deal with top Senate Republican to protect legalized marijuana states
Scotland Yard said officers were working to formally identify the victim and that an investigation had been launched. It is believed the two knew each other.