Governing body FIA said 31 people were treated by Catalunya Circuit medical staff with seven of those flown out to a variety of hospitals to receive treatment.
Catalonia's regional government said in a statement that one of the persons was airlifted to Barcelona hospital with serious burn wounds while the rest were being treated at local hospital for smoke inhalation.
Williams confirmed a fuel leak caused the problem, with four of its staff treated for injuries. Three of those remained in hospital.
F1 team Caterham said in a statement that four team employees were among those taken to the Catalunya Circuit medical centre to be examined, one with a minor hand injury and three with respiratory issues.
The fire erupted soon after Maldonado and the team had taken the traditional victory photo in front of the team garage with members of all teams close by rushing to help contain the blaze.
"The FIA is collaborating closely with the Spanish authorities investigating this incident," FIA said.
Williams team principle Frank Williams, who is a paraplegic, was rushed from his wheelchair as he was giving a celebratory speech for a first F1 victory in eight years that coincided with the longtime team principal's 70th birthday celebrations.
A black, acrid haze came flowing out of the British team's garage, filling the paddock and pit lane.
Mechanics and circuit firefighters were quickly on the scene to put out the fire with an ambulance on the scene treating one person for what appeared to be smoke inhalation.
Williams driver Bruno Senna's car was torched by the blaze, while Maldonado's car was alongside fellow podium finishers cars away from the Williams garage.
Paul Logothetis can be reached at: www.twitter.com/PaulLogoAP