"So far, we understand that the car involved was a taxi that drove to the hospital just before the explosion," Merseyside Police Chief Serena Kennedy said at a news conference, according to the Liverpool Echo.
The men are 29, 26 and 21 years old, reports The Guardian.
The deceased man was a passenger in the taxi.
The driver is being cared for in hospital.
The explosion took place at eleven o'clock in the morning local time and the area is kept cordoned off.
During the day, a bomb squad has been on the scene, but it is unclear whether it has needed to assist the criminal investigators.
The hospital in question mainly receives female patients, but due to the explosion does not receive any at all at the moment.