Royal Dutch Shell said it had contained a fire at its 500,000 barrel-per-day (bpd) refinery in Singapore.
The company said all its staff were accounted for and non essential staff had been evacuated to safety.
"We believe it was an accident. A full investigation will be conducted once the fire is put out," Shell said.
Neighbouring units were shut down as a precaution. In the process of a shutdown, Shell advised that a larger flare would be visible and that the flare was no cause for alarm, as no toxic vapours were being released.
One Shell firefighter sustained a superficial injury, and five other firefighters had heat exhaustion and pulled muscle, the company added.
Shell had earlier said it shut some units at its refinery after the fire.
(Reporting by Naveen Arul in Bangalore)