Lightning struck a huge oil storage facility Friday at a port in the southern Malaysian state of Johor, causing at least one tank to explode and two others to catch fire, an official said.

No casualties were reported. At least 5,000 workers have been evacuated and the area surrounding the fuel depot at the Pasir Gudang port has been cordoned off, a municipal official said on condition of anonymity in line with policy.

Fire department officials battled the blaze. The oil tank farm also houses petroleum products belonging to U.S. companies Caltex and ExxonMobil, the official said.

The five-story storage tank that caught fire belonged to national petroleum company Petronas, and the blaze spread to two other tanks, an official said.

In a brief statement, Petronas said the depot stored fuel and petroleum products, and served the southern region in Malaysia bordering Singapore.

"The company has made arrangements for the products to be sourced from its other depots," Petronas added.

It was not immediately clear how much oil was lost. Already jittery oil traders are on the lookout for any supply glitch that could add to geopolitical uncertainty that has sent benchmark crude oil past the $70 a barrel mark recently.