A torchlit prayer march in response to a spate of fatal shootings in south-east London attracted more than 2,000 people.
Demonstrators walked from Peckham to Brixton in the rally organised by local church and community leaders.
As the march reached Brixton's Windrush Square, police estimated that the crowd had grown to about 1,000.
Five people - including three teenagers - have been murdered in south London in the last month.
The walk took protesters across Southwark and Lambeth, the two boroughs where the killings took place.
Pastor Nims Obunge said: "Drugs and guns are a menace to our society.
"We all need to work together with criminal justice agencies to help vulnerable young people and keep guns off the street."
Lee Jasper, equality advisor to London mayor Ken Livingstone, said the march "demonstrates the total abhorrence" to gun violence in the city.
"Our children need to see we care," he said.
"We must support the police tackling these crimes. We must also face the reality that we have a serious problem with a small minority of our young people."
The march took place as Prime Minister Tony Blair hosted a gun crime summit at Downing Street.
Mr Blair has suggested the minimum age at which someone faces a mandatory five-year jail sentence for possessing a gun could be reduced from 21 to 17.
Three teenagers have been shot dead in the last month.
Michael Dosunmu, 15, was shot dead by two gunmen in his Bedroom in Peckham on 6 February.
Eight days later Billy Cox, also 15, was murdered in home in Clapham North.
On 3 February, James Andre Smartt-Ford, 16, was shot dead at Streatham Ice Rink.