Among the 12 officials arrested are the chairman and vice chairman of the logistics company that owned the warehouse where the blasts that killed 139 people originated from - they are suspected of illegally storing dangerous materials according to state news agency Xinhua.
Chinese authorities said on Tuesday that 135 people were now known to have died as a result of the explosions in Tianjin last week, including 81 firemen.
38 people are still missing and 582 people are still in hospital.
Xinuha news agency published an investigative report on Wednesday in which it questioned the legitimacy of the fire, safety and environmental approvals given to the warehouse that exploded last week, killing at least 114 people.
The report says that the two largest shareholders in the company that owned the warehouse used their political connections to secure the approvals despite the storage facility being within 560 meters of residential buildings.
The official death toll from the explosions that rocked the Chinese port city last week still stands at 114 but 65 people, among them 49 firefighters, are still unaccounted for.