Just before 12:30 a.m., the plane, a Canadair CRJ 200, sent out an emergency signal over Swedish territory, according to news agency TT.
"But they sent the mayday for a very short time, then the plane disappeared from our radar," Daniel Lindblad, in charge of press at the Swedish Maritime Administration, told TT.
Swedish and Norwegian ambulance and rescue helicopters, as well as the Norwegian air force, were sent to help with the search.
Lindblad said that just after 3 a.m., the Norwegian air force found the wreckage, and he added that he didn't dare say at this point whether there was any hope that anyone had survived, and the CEO of the airline company, West Atlantic in Gothenburg, told TT that two pilots were missing.
Gustaf Thureborn, the CEO of West Atlantic in Gothenburg said this morning that this was the first time in the company's history that it had held a press conference about an accident.
"We know only that we're missing an airplane with two of our pilots and four and a half tons of freight - mail and parcels," Gustaf Thureborn, the CEO of West Atlantic, told TT.
According to the company, the captain on board was listed as 42-years-old and based in Spain, and the first officer 34-years-old and French. Both have over 3,000 flight hours.
The plane is said to have been flying for the Norwegian postal service, but was registered in Sweden.
Only small fragments remain of the plane, according to Lindblad, which was found by a Norwegian F-16 that came to aid the Swedish rescue operation on a plateau between the northwestern part of the Akkajaure reservoir and the Norwegian border.
As yet, the cause of the crash is unknown, but Lindblad said that there were no difficult weather conditions.
The Swedish Accident Investigation Authority met this morning and aims to send investigators to the site of the accident by tomorrow morning. The acting director general Jonas Bäckstrand is heading up the investigation and said they would try to find the plane's black boxes, adding that so far, they haven't found anything abnormal about the flight. He told TT that he sees no similarities to the Norwegian Hercules plane that crashed at Kebnekaise in 2012, other than that both plane crashes happened in a mountainous area. While the Hercules flew into the side of a mountain, he said something happened on this plane, even if it's unclear what.