Detectives fear a gang of arsonists could be randomly targeting homes after a spate of petrol attacks.
Investigators believe the same gang is behind four attacks over three days in New Cross, south east London.
In each incident petrol was poured through the letterbox of a home as well as over the front door or window before being set alight.
The suspects wore dark clothing and covered their faces with hoods during the attacks, one of which took place in the afternoon.
Detective Inspector Steve Heatley, who is leading the inquiry, said he fears somebody could die unless the culprits are caught.
He said police have been unable to find a link between the attacks and they may be entirely random.
Mr Heatley said: "We think they are linked but we do not know why. It is because of the modus operandi, pouring petrol through the letterbox, which is quite unusual. It also just so happens that they are in the same area.
"It concerns me because fire can kill innocent members of the public and it spreads very quickly. I want to make people aware."
The first two arson attacks took place in Primrose Walk, near Fordham Park, shortly after midnight and at 9.10am last Sunday.
The third attack took place a short distance away in Balborough Street at 2.30am on Monday and the fourth in Nettleton Road on Tuesday at about 4pm.
Police said no-one has been injured in the four attacks and damage has been "minimal".
Six men aged between 18 and 27 arrested in a vehicle in Eastdown Park, Lewisham, shortly before midnight on Wednesday remained in police custody today.
Anyone with information should contact Lewisham Police on 0300 123 1212 or Crimestoppers anonymously on 0800 555 111.Reuse content