Tragedy struck near Galveston on Monday when a small aircraft belonging to the Mexican Navy, carrying a young medical patient and seven others, crashed, resulting in at least five fatalities. The incident spurred a wide-scale search in the waters off the Texas coast.

Aboard the ill-fated flight were two representatives from the Michou and Mau Foundation, a nonprofit organization dedicated to supporting Mexican children suffering from severe burns.

The crash occurred in the afternoon near the base of a causeway—a type of elevated roadway usually constructed over water—along the Texas coastline, roughly 50 miles southeast of Houston. The cause of the crash remains under investigation.

In an official statement, Mexico’s Navy confirmed the aircraft was engaged in a medical mission when it experienced an “accident.” The Navy has pledged to conduct a thorough investigation into the cause and is actively collaborating with local authorities on the ongoing search and rescue efforts.

Officials from the Federal Aviation Administration and the National Transportation Safety Board have arrived at the crash site, according to a post by the Texas Department of Public Safety on the social platform X.

A spokesperson from NTSB said they are “aware of this accident and are gathering information about it.”

The Galveston County Sheriff’s Office said officials from its dive team, crime scene unit, drone unit and patrol were responding to the crash. It said in a post on Facebook that the public should avoid the area so emergency responders can work safely.

Galveston is an island that is a popular beach destination.

It’s not immediately clear if weather was a factor. The area has been experiencing foggy conditions over the past few days, according to Cameron Batiste, a National Weather Service meteorologist. He said that at about 2:30 p.m. Monday, a fog came in that had about a half-mile visibility.