(CNN) -- An explosion hit an oil platform on Lake Pontchartrain in Louisiana Sunday night, injuring seven people and possibly leaving one person unaccounted for, according to Jefferson Parish President Mike Yenni.
Nearby residents reported hearing what sounded like a "sonic boom" coming from the lake at 7:19 p.m. local time, at which point the city's fire department was dispatched to investigate, said Ben Zahn, mayor of the city of Kenner.
The platform, which is a storage and transfer structure for oil wells on the lake, was still burning, Jefferson Parish Sheriff Joe Lopinto said at a press conference late Sunday.
The seven injured people were taken to the hospital.
Search-and-rescue efforts were underway for one person who was working on the platform but was unaccounted for after the explosion, Lopinto said. Authorities said that they were working to confirm exactly who was on the platform at the time of the explosion.
"We believe there's still one unaccounted for, although we're dealing with subcontractors and we're trying to get names of everybody to make sure," Lopinto said. "We are treating it as having one person unaccounted for and treating it as a search and rescue."
It was also unclear but likely that oil was spilling into Lake Pontchartrain, said Chief Dave Tibbits of the East Bay Consolidated Fire Department.
Officials were trying to find the valve to shut off what they believe is oil leaking into the lake.
Jefferson Parish's water supply comes from the Mississippi River and no drinking water comes from Lake Pontchartrain, Yenni said.
What caused the blast is unclear, but fire investigators are looking at the possibility of a combination of chemicals that may have ignited on the platform and led to the explosion.
"The good news is that the platform is close to shore and Lake Pontchartrain is shallow and the lake is calm and there are no winds," said Carlton Dufrechou, director of the Lake Pontchartrain Causeway, at the press conference.
Based on that assessment, the situation was expected to be contained relatively quickly, he added.