The Mexican Navy said at least two people were killed on Monday when one of its medical aircraft crashed into Galveston Bay in Texas.

The aircraft, a King Air ANX-1209, was carrying four civilians and four crew members, the navy said. By Monday afternoon, and in coordination with the U.S. Coast Guard, the Mexican Navy had rescued four people and recovered two bodies. Efforts were continuing to rescue two more people who were aboard, the navy said.

In a statement, the Mexican Navy said its aircraft was carrying out a medical support mission with the Michou and Mau Foundation, a nonprofit that assists Mexican children with severe burns. The aircraft, the navy said, “experienced an incident” upon approach to Galveston.

In a statement posted to social media, the Galveston County Sheriff’s Office said that it was assisting at the scene, and that the Texas Department of Public Safety was leading an investigation into the crash. The area was experiencing heavy fog on Monday.

The U.S. Coast Guard said that its watch standers received a call at about 3:17 p.m. reporting a plane crash west of the Galveston Causeway, with eight people aboard. The Coast Guard said it responded to the scene with a rescue boat and helicopter. The Galveston Police and Fire Departments, Beach Patrol and life guards were also assisting, the Coast Guard said.

Flight record data shows that the plane flew from Mérida, in the Yucatán Peninsula, to Galveston. The cause of the crash is under investigation.

The Texas Department of Public Safety directed inquiries about the crash to the Federal Aviation Administration, which did not immediately respond to a request for information. The sheriff’s office also did not immediately respond to requests for information on Monday evening.

This is a developing story.