Authorities say 57 others, including 39 firefighters, were injured in the explosions near the capital, Bucharest.
The firefighters were injured in a second explosion as they were helping douse the fire in Crevedia commune, north of the capital, according to the government. At least 10 of those wounded were in critical condition, according to hospital representatives and local media.
About 25 fire engines were at the scene to bring the blaze under control, Romania’s emergency situations inspectorate said.
Prime Minister Marcel Ciolacu said the injured might be sent abroad for treatment.
“We think four of the patients will more than certainly be transferred tonight to hospitals in Italy and Belgium,” Ciolacu told reporters after an emergency meeting with the state agencies involved in handling the crisis.
Ciolacu attended a crisis cell meeting at the Ministry of Internal Affairs after the explosion.
About 3,000 people within an 800-metre (875-yard) radius have been evacuated, according to the ministry.
“The area needs to be assessed. The area is still dangerous … There is a risk of another explosion at another tanker,” Raed Arafat, head of Romania’s emergency department, told Digi24 television.
President Klaus Iohannis described the incident as a “tragedy”. “I’m profoundly saddened that the explosions in Crevedia resulted in victims,” he wrote on Facebook.
“An investigation must quickly be launched to see if rules were broken. I ask the authorities to take urgent measures for the injured so that these tragedies won’t happen again,” he added.
Anger has flared repeatedly in the European Union member state over a lack of official oversight over safety measures.
In 2015, a blaze ripped through a Bucharest nightclub after fireworks were let off, killing 64 people.