Fire was seen raging above the plant and thick smoke billowed into the sky above for more than an hour, according to an online video posted on YouTube. Residents from several kilometres away were able to view the explosion.

The fire broke out at 10.35pm local time in the Siaogang district. The city’s fire department said flames were put out early today and no one was injured or trapped as per an initial investigation.

CPC spokesman Ray Chang said there was “very limited impact” on the company’s output, as it has several other such units in its facilities across the island.

“We are moving quickly to look into the cause of the incident and make improvements,” Chang said, adding that an initial probe pointed to gas leakage but further checks were needed.

Kaohsiung mayor Che Chi-Mai asked CPC to suspend its operations at the plant until an inspection was completed, adding that labour and environmental authorities have imposed a total fine of T$5.3 million (US$165,098.75) on the company.

The fire occurred at the resid hydrotreater No 3 unit, CPC’s Chang said. The unit, which has a capacity of 40,000 bpd according to Refinitiv Eikon, is used to remove sulphur from oil products.

The incident happened during routine maintenance at the plant, the city government said.