Six fire engines and around 40 firefighters were called to a fire at a restaurant with flats above on Barking Road in Plaistow.
Part of the ground and first floor of the three-storey building were damaged by the fire and the ducting from the ground to the first floor was destroyed. One woman and two children were treated at the scene for smoke inhalation and taken to hospital by London Ambulance Service crews.
Station Commander Dave Reed, who was at the scene, said: "The fire spread through the restaurant's ducting system and smoke spread through an open door to properties next door.
"Firefighters wearing breathing apparatus rescued seven people from the first floor via an internal staircase.
"There were local road closures in place and some bus routes were diverted. We advised people to avoid the area where possible."
The fire is believed to have been accidental and caused by a build up of oils and fatty deposits inside the ducting which ignited.
A London Fire Brigade spokesperson said: "We'd like to remind restaurant and takeaway owners to ensure they don't have dirty ducting.
"If you don't clean the ducting in your extraction system regularly, you're at a greater risk of ducting fires.
"You should also make sure you keep the hob, cooker hood and extractor fan clean too – built up fat and grease can ignite and cause a fire."
The Brigade's 999 Control Officers took 13 calls to the blaze.
The Brigade was called at 0948 and the fire was under control by 1102. Fire crews from Plaistow, East Ham, Stratford, Poplar, Barking and Mill Wall fire stations were at the scene.
Firefighters tips for restaurants and takeaways