Firefighters in Singapore are battling a massive blaze at a major oil refinery for a second day Thursday.

The fire broke out Wednesday at the Palau Bukom island, forcing the evacuation of hundreds of non-essential employees. Officials with the Singapore Civil Defense Force say there has been a “surge” in the fire at the plant, but it remains contained in a specific area.

The refinery is operated by energy giant Royal Dutch Shell. It produces 500,000 barrels of oil per day, making it Shell's largest refinery.