President Xi Jinping urges 'all-out efforts to rescue victims and extinguish fire,' as a blaze continues to rage at the site.
Plumes of smoke still billowed over buildings hours after the explosion, which occurred around 11:30 pm (1530 GMT) local time Wednesday, August 12.
"The fireball was huge, maybe as much as 100 meters tall," said 27-year-old Huang Shiting, whose house is close to the port area of the city where the explosion took place.
"I heard the first explosion and everyone went outside, then there was a series of more explosions, windows shattered and a lot of people who were inside were hurt and came running out, bleeding," he told Agence France-Presse.
State broadcaster CCTV said 17 people were killed and more than 400 hospitalized, adding in a Twitter post that President Xi Jinping had urged "all-out efforts to rescue victims and extinguish the fire".
State news agency Xinhua confirmed the death toll, and said 32 people were critically injured.