More than 100 police and emergency personnel were deployed to the scene of the blast on Monday evening.
Harri Richie, who lives around 100m away from the targeted building, told the BBC she heard an “unbelievably loud explosion” at about 21:00 local time from the underground car park she was in.
She then went up to her 11th floor apartment, where she said she saw emergency services “dragging two people out [from the building] who looked badly injured”.
Emergency services arrived around five minutes after the explosion, she said, adding that there was a helicopter overhead throughout Monday night.
“This is the first time in history, to my knowledge, that such an act has taken place in the principality,” Mirmand, the head of Monaco’s government, said.
Monaco’s Prince Albert II described the incident as a “heinous crime” and “a shock to the entire Monaco community”.
He said “all concerned state services are currently being mobilised” in co-operation with the relevant French authorities.
Yermolaiev is a 58-year-old wealthy real estate developer from Dnipro, Ukraine’s fourth-largest city, who has been living in Monaco.
He is now a Cypriot citizen after renouncing his Ukrainian citizenship in 2019.
He has big interests in the wine and alcohol business in Russian-annexed Crimea, and since 2023 has been the subject of sanctions imposed by the government in Kyiv.
He was named the 39th richest Ukrainian by Forbes magazine in 2020, with a fortune of $230m (£173.8m).
