Fighter planes were dispatched by NATO when a private jet carrying four people strayed off course and crashed off the coast of Latvia, according to authorities.

According to FlightRadar24, the Austrian-registered Cessna 551 aircraft took off from Jerez in southern Spain at 12:56 GMT without a predetermined destination, as reported by Reuters.

It made two turns at Paris and Cologne before flying directly over the Baltic and passing close to the Swedish island of Gotland. At 17:37 GMT, the flight tracker indicated that the aircraft was quickly losing speed and altitude. 

The pilot, a man, a woman, and a kid aboard the aircraft reported cabin pressure difficulties to air traffic control, the German daily Bild said.

Occasionally, the aircraft flew erratically, making two turns near Paris, France, and in Cologne.

According to FlightRadar24, it then flew across the Baltic Sea, passing near the Swedish island of Gotland.

At 7:37 p.m. local time (1737 GMT), the flight tracker indicated that the airplane was quickly losing altitude and speed.

Just before 8:00 p.m., the plane fell into the water off the coast of Ventspills, according to Agence France-Presse.

The Latvian civil aviation agency said that air traffic authorities were unable to make communication with the aircraft.

Fighter aircraft from Denmark, Sweden and Germany were dispatched to make visual contact with the crew, but "they saw no one," according to the head of the Swedish search and rescue effort, Lars Antonsson.

Antonsson said the plane flew pretty steadily until it approached the shore of Latvia, at which point it suddenly dropped height and crashed "due to a lack of fuel."

"No human remains have been located, and although the cause of the plane's deviant flight is unknown, they were obviously incapacitated on board," Antonsson said.

Hans Kjall, an expert on aviation safety, told the Swedish news agency TT that cabin pressure issues may have caused passengers to lose consciousness.

He said that this can occur rapidly at heights where tiny planes are operated.

The Swedish Coast Guard reported discovering traces of oil and smaller debris in the water.

A Lithuanian air force helicopter has been rushed to the crash location, according to a military official.

The Latvian Navy has dispatched ships to the scene. According to the MarineTraffic website, a Stena Line ferry heading from Ventspils to Norvik in Sweden was also rerouted to the collision site.

The webpage also displayed a Swedish search-and-rescue helicopter and aircraft on the scene.