The Hilton Hotel in Mayfair went up in flames just after 6.40pm (BST), leading to a full evacuation of its 1,500 guests.
Liza Minnelli is also thought to have been among those taken from the building, according to BBC News.
Earlier in the day, the stars had been attending the Nordoff Robbins O2 Silver Clef Awards at the hotel, where Lennox was honoured for her outstanding contribution to music. Other winners included Biffy Clyro, Tinie Tempah and Arcade Fire.
The London Fire Brigade brought the blaze under control by 11pm last night and small groups of guests were allowed back into the hotel by 3am today (2) as part of a “phased reoccupation”.
The London Ambulance Service confirmed that there had been no fire-related injures, although an elderly guest had to be treated by paramedics after falling ill.