A spokesperson for the police said Westminster officers responded on Monday to a hotel where a "46-year-old woman was pronounced dead at the scene".
A police spokeswoman on Tuesday said the death was "not being treated as suspicious".
Celebrities took to Twitter to express their grief over the death, the reason for which wasn't immediately revealed.
Music producer Dan Waite, a friend of O'Riordan's, said she had left him a voice message shortly before her death "stating how much she loved the Bad Wolves' version of Zombie; she was looking forward to seeing me in the studio and recording vocals".
O'Riordan was forced to cancel most dates on a tour with the reformed band previous year because of a bad back.
"She sounded full of life, was joking and excited to see me and and my wife this week".
"Family members are devastated to hear the breaking news and have requested privacy at this very hard time", the statement added.
The Hilton hotel in London's Park Lane confirmed that a guest had died on the premises. "The news of her passing is devastating", he said.
"For so many of us, especially those of us who grew up in the 1990s, she was the voice of a generation". "She blazed a trail across the world with her unique voice and also her talents in songwriting and our thoughts are with her, her family, her friends and people of Limerick in particular".