Officers were called to the double shooting in Wodehouse Avenue, Peckham, just before 8pm on Saturday.
Metropolitan Police said the men – believed to be in their 20s – were taken to hospital, where one remains critical.
The other man’s injuries are not thought to be serious, the force added.
Armed officers were sent to the scene and an air ambulance landed at a playground nearby, while a car was pictured at the scene with a shattered driver’s window.
A section 60 order, which temporarily allows police to stop and search people without having reasonable grounds, was put in police in the area until 7am on Sunday.
Meanwhile, in Greenwich, a man believed to be in his 40s was found with multiple stab injuries in Claremont Street shortly before 6.50pm and taken to a south London hospital.
No arrests have been made and enquiries are ongoing.
More from London
Murder investigation launched after man stabbed to death in Chelsea
Parents’ desperate plea for tougher punishments for drivers using phones
YouTube deletes more than half of violent music videos flagged by Met
Reece Williams charged with ‘brutal’ murder of Marcel Campbell in north London
Electric storm lights up London landmarks
UK struck by lightning 60,000 times in 24 hours
The incidents are the latest gun and knife incidents in the capital and come as detectives charged a man with the murder of a 28-year-old woman in Brent, northwest London.
Residents in Croydon have also spoken of their fears after a man was filmed attacking a motorist with a 15-inch knife.