Four people died and two were missing after a helicopter crashed en route to a Chevron oil platform off the Angolan coast, Chevron said on Tuesday.

The helicopter left Malongo port in Angola’s Cabinda province on Monday at 1523 local time to make the short journey to the Tombua-Landana offshore oil platform but never arrived.

“The helicopter did not reach its intended destination. It was carrying five passengers and one pilot,” Chevron said in a statement, adding that one of the passengers was an employee while four others were contractors.

“Extensive search and rescue activities continue for those who remain missing.”

Chevron did not say if there was any impact on oil production from the crash or the search and rescue operation, which involved 19 marine vessels and three helicopters.

Angola competes with Nigeria to be Africa’s largest oil exporter, shipping around 1.7 million barrels per day, mainly to Asian markets.