A criminal investigation has been launched and police and fire investigators are treating the blaze as suspicious.
Witnesses today said a man had been run into the temple during a women-only prayer session then escaped just before flames were first seen.
Having spotted the intruder, the 10 women quickly discovered the fire, which had taken hold in one of the holiest parts of the temple. They tried to put it out but were beaten back by the flames.
Witnesses described the suspected arsonist as being black or mixed-race.
Most of the temple's roof collapsed and worshippers fear all but one of its eight holy books were destroyed.
More than 50 firefighters battled the fire for almost eight hours after the being called just after 2pm yesterday.
A witness, Gurpal Singh, 35, an IT worker from Chingford who worships at the temple, said: "Somebody did this deliberately. A man came in and got to the temple's holiest area. He was interrupted by one of the women and managed to get away. As he ran out, the place went up in flames. Everyone panicked. The women tried to put out the fire with buckets of water but it was too fierce."
Mr Singh said the women managed to save one of the temple's holy books, but the flames took hold before they could get to the other seven.
"I can't describe how important those holy books were to the Sikh community," he added. Kulvinder Singh Virk, 26, who runs a local off-licence and is also a member of the temple, said: "This is very personal for us. It's as if a member of our family has been burnt to death."
Kamaljet Kaur, a 24-year-old from Stamford Hill, said her aunt was in the temple when the alleged arsonist struck.
She said: "All the women thought he was a robber. It was only when they got upstairs that they discovered the fire raging. It is lucky one of them wasn't badly hurt."
"Often, more than 200 people worship here. Thankfully it was a quiet day."
The London Fire Brigade confirmed that 75 per cent of the building and the roof had been damaged by the fire.
One worshipper said that in the past few weeks he had noticed racist graffiti on one of the temple's outer walls.
A Met spokesman said: "Police are treating this incident as suspicious."
The temple opened in 1979 and has been a vital part of the Sikh community. The building, which dates back to 1854 was formerly a synagogue and before that a chapel.