KUALA LUMPUR - Two men were injured after a fire and explosion occurred early on Friday morning (April 12) at an oil refinery being developed by Malaysian oil firm Petronas in Johor.

Petronas said the incident occurred at 1.25am at the Pengerang Integrated Complex. It said its emergency and fire response team was deployed and the fire contained within 30 minutes.

"The situation is under control and all relevant authorities have been informed," it said. "We will provide additional information in due course, as the investigation is still being carried out."

Police said two men, who were locals aged 28 and 30 and believed to be working as security guards at the site, were injured in the incident, The Star reported.

Bernama reported that more than 10 houses in Kampung Lepau near Pengerang were believed to have been damaged.

Kota Tinggi district police officer Ashmon Bajah confirmed the incident, saying that the fire took place at one of the project sites within the complex.

"The Petronas (emergency and response team) received the report and deployed five fire engines with 30 firemen, and they were able to control and put out the fire at around 2.15am," he said. "Two locals, who work as security personnel at the site, were injured and have received outpatient treatment at the Rapid Pengerang emergency centre."

He added that a joint investigation was currently underway to determine the cause of the fire.

Singapore's National Environment Agency said in a Facebook post around noon on Friday that it is closely monitoring the situation and air quality in the Republic in relation to the explosion.

It added that the 24-hr PSI has been in the low-moderate range since 1am, while the 1-hour PM2.5 readings remained in Band I (Normal). Ambient levels of volatile organic compounds along Singapore's coast also remain within safe levels.

NEA said it is in contact with the Department of Environment (Johor) and will provide updates if there are changes to the situation.

Media reports suggested that the explosion was triggered by a leaking gas tank.

Comments on social media have suggested that the blast caused tremors that could be felt by residents of nearby residential areas and as far off as Pasir Gudang, located about 50km away.

Video footage allegedly of the incident has been circulating online, showing a large fire and thick smoke rising up to the sky from the facility.

Mohd Azizi Mahmun, 24, who lives in nearby Taman Ramunia Indah in Pengerang, said he felt as though there was a strong "kick" on the door of his house when the incident occurred. "I was asleep during the incident, and woke up due to the strong vibration," he told Bernama. "It also set off car alarms in the area. My neighbours and I then came out (of our houses) and saw smoke and fire in the area," said Mohd Azizi, who is the site coordinator for a company at the complex.

In Kampung Lepau, about 1km from the Petronas facility, home owner Abd Rahim Sanusi, 85, said he was awakened when he heard the loud explosion, Bernama said.

"I have just undergone heart surgery, and was shocked (by the blast). When I got out of the room, I saw much of the ceiling in my house had come down," he told Bernama.

He said there were also several cracks in the walls around the house.

Another villager, Abdul Halim Mahmood, 52, said he was just about to go to sleep at about 1.30 am when he heard a loud sound like that of a bomb exploding.

"I heard the sound of glass breaking, so I looked outside and found that my sliding door had shattered," he said, adding there were also cracks in some of the walls.

Village chief Zainal Abidin Abd Rahim said he received calls from the other villagers. "Shortly after the incident, I contacted a Petronas representative to find out what had happened.

"Petronas then asked me to check each home to identify the types of damage incurred, and for those affected to lodge police reports," Bernama quoted him as saying.

Bernama reported that the situation had returned to normal, with no trace of smoke left visible by 6.30am. It said a visit to the complex showed that it was operating as usual, with buses carrying workers and lorries heading in and out of the premises.

Reuters news agency reported that the refinery was testing its facilities ahead of planned commercial operations later this year. It said the complex will be anchored by Rapid, or Refinery and Petrochemical Integrated Development, and is Petronas' biggest domestic investment in a 50-50 joint-venture with Saudi Arabia's state-owned Saudi Aramco.

Petronas is currently testing its systems at Rapid, running crude oil through its fuel processing units and labyrinth of pipes and producing large exhaust gas fires from its flare tower, Reuters reported.

The refinery, which will process around 300,000 barrels per day of crude oil once fully operational, is expected to come online later this year, and sell fuel to customers in Malaysia and across South-east Asia.