Li Liang, the president of Tianjin Dongjiang Port Rui Hai International Logistics Co, which stores and transports chemicals, was among those being held, as was the company's vice president, Cao Haijun, and Song Qi, the chief financial officer.
They have been under detention since August 13. Earlier reports had said two unnamed executives of the firm were in detention.
Massive explosions rocked the northeastern coastal city late Wednesday, killing at least 114 people, officials said, and devastating a large industrial zone and nearby residences.
At least 65 people are still missing, according to the latest figures from authorities.
Thousands of officials, firefighters, policemen and local residents mourned the victims at the blast site Tuesday, bowing their heads and observing a moment of silence to pay their respects.
China also said it was investigating the director of the country's work safety agency, Yang Dongliang, who was also Tianjin's vice mayor until 2012.
Yang was being investigated for "severe violation of discipline and law", the Chinese Communist Party corruption watchdog said, but didn't directly link the probe to the disaster.
Questions over license
Official news agency Xinhua said the company was licensed to handle dangerous chemicals
at the time of the blasts but only obtained that license in June. A previous license had lapsed in October 2014.
The warehouse was a temporary storage facility that housed materials after they arrived at the port and before they were transported elsewhere, city officials have said.
Several hundred tons of sodium cyanide, a highly toxic chemical that can kills humans rapidly, have been found at two locations and are being cleaned up, they added.
Residents in Tianjin with homes near the blast site have shared their concerns about the long-term environmental and health consequences of the blasts.
A CNN team in the city says barrels of unknown chemicals propelled by the explosions remain close to residential areas and they witnessed chemicals reacting with rain water, emitting white steam.
Bao Jingling, chief engineer of Tianjin Environmental Protection Bureau, said Wednesday that air quality outside the blast zone was normal and the cyanide concentration in tested water and soil was in normal range.
However, cyanide was detected over limit at eight water monitoring spots inside the warning zone, with levels at one spot exceeding limits by 277 times. Bao said that this was at the outlet of a blocked pipe and wouldn't pollute surrounding areas.
China's State Council has formed an investigative committee to "give a responsible answer" on the cause of the disaster and promised "serious punishment," Xinhua reported Tuesday.
"Many are questioning about the number of people killed in the blasts, the emergency assistance provided, and the handling of the aftermath. Some are even suspicious, with rumors circling," said a commentary in the People's Daily, the Chinese Communist Party's mouthpiece.
"In the face of an accident that has caused heavy losses of life and property, the central government's attitude is clear and resolute: a thorough investigation and severe punishment are beyond any doubt," it concluded.
The explosions are also taking their toll on business in the port city.
Japanese car maker Toyota said that it had been forced to halt production at three production lines in the city, with one factory located just 3 km from blast site.