Witnesses have reported the hotel and neighbouring restaurant being evacuated and chemical response teams on the scene.
One witness told Daily Star Online everyone staying at the hotel has been “quarantined”.
She said: “My husband has just been advised by police that they found someone dead with unknown chemicals.
“Until they figure out what they are they can’t give any more information.”
Eight police cars, six fire engines and eight embulances are on the scene – as well as officers in hazmat suits.
Daily Star Online understands the substance discovered at the hotel is believed to be Fentanyl.
Fentanyl is a painkiller 50 times more potent than morphine, it is highly addictive and linked to the drug crisis in the US.
In a statement, the Met Police said: “Police were called at 2.44pm Thursday, 6 June by staff to a hotel in Leisure Way, N12.
“A women in her 30s was found unresponsive by staff in the building.
London Ambulance Service attended and the female was pronounced dead at the scene.
‘Efforts are ongoing to identify the woman and inform next of kin.”
The spokeswoman added: “Her death is currently being treated as suspicious.
“Officers from North West Command Unit remain on scene. Enquiries continue.
“Following the discovery of a substance, guests and staff were evacuated as a precaution.
“There are no serious injuries. Not terror related.”