Drone strikes have sparked huge fires at two major oil facilities in Saudi Arabia run by the state-owned company Aramco.
Apocalyptic scenes were caught in footage from Abqaiq, the site of Aramco's largest oil processing plant.
The huge fire engulfed multiple sections of the site, which is the world's largest oil processing plant ad employs a number of Western workers.
The man who filmed the footage, who declined to be identified, said he was woken up by the noise coming from the refinery.
A second drone attack started fires in the Khurais oilfield, which is the country's second largest oilfield.
Yemen's Iran-aligned Houthi group have been blamed for the attack in the latest flare up of violence in the Gulf.
Riyadh accuses Iran of arming the Houthis, a charge denied by the group and Tehran.
Tehran denies the accusations.
Saudi Arabia said it had brought the blazes under control but three sources close to the matter said oil production and exports had been disrupted.
One source said five million barrels per day of crude production had been impacted close to half the kingdom's output, but did not elaborate.
The precise targets and the extent of possible damage were unclear and authorities have not reported on casualties.
The Saudi interior ministry spokesman said Aramco industrial security teams were fighting the fires since 4am (2am BST).
The Houthis' military spokesman said the attacks hit refineries at both sites, which are over 1,000 km from the Yemeni capital Sanaa, and pledged a widening of assaults on Saudi Arabia.
The chief of Iran's elite Quds Force, Qassem Soleimani, in a rare reaction to such attacks on Saudi Arabia, praised the Houthis for their resistance in a Twitter post that included the hashtag Aramco.
Tensions are running high in the region after attacks in June and July on oil tankers in Gulf waters that Riyadh and Washington blamed on Iran.
The United States quit an international nuclear deal and extended economic sanctions on Iran.
The Houthis hit Shaybah oilfield last month and two oil pumping stations in May.
Both attacks caused fires but did not disrupt production.
The coalition has responded with air strikes on Houthi targets in Sanaa and other areas held by the group, which controls most large urban centres in Yemen.
The violence is complicating U.N.-led efforts to ease tensions between the Houthis and Riyadh to pave the way for political talks to end the war, which has killed tens of
thousands of people and pushed millions to the brink of famine.
Aramco did not immediately respond to a request for comment.
