The two helicopters had taken off from Estonia and collided near Eura, western Finland. There were no survivors.

Close cooperation will be maintained with Estonian authorities, Finland has said.

Robin Lardot, head of the Finnish Criminal Police, said at Sunday's press conference, held in Turku, that police have begun investigating the causes of the accident, with the investigation focusing primarily on the distance maintained between the two helicopters during the flight, and their altitude at the moment of the collision.

Police have already questioned eyewitnesses and those near the scene, and evidence started to be gathered from the scene on Saturday.

The remains of the two helicopters, both Robinson R-44 models, have also been sent to Turku for more detailed investigation. Autopsies of the deceased are also to take place in Turku.

One of the helicopters was largely burned out, it is reported.

Taking part in the press conference was Tuomas Kiskola, head of the local rescue service, who said notification of the accident was received at 12:37 p.m. on Saturday, while the first helicopter was located at 12:58 p.m., the second at 1.24 p.m.

All occupants of both helicopters were pronounced dead at the scene, Kiskola stated. The investigation was handed over to the police shortly before 3.45 p.m. on Saturday.

Chief Commissioner of Finland's National Bureau of Investigation Olli Töyräs said at the press conference that Finnish police have already started cooperation with Estonian police and officials to obtain data needed for the investigation, stressing that it is in its early stages.

Investigators say they also hope to receive information from Estonia about the individuals on board, and the backgrounds of both pilots.

Tiina Bieber, of the Finnish Safety Investigation Authority, said that their personnel began work at the crash site on Saturday afternoon and are continuing throughout the Sunday.

It is not currently viable to say whether the cause of the accident was the result of human error or a technical malfunction, she added.

The investigation may take up to nine to 12 months, Bieber stressed.

Among the deceased in Saturday's accident were businessmen Oleg Sõnajalg and Priit Jaagant, and the wife of the latter, Lilit Jaagant.

Postimees has reported that another of the victims was motorsport competitor Tiit Kuusk.

Finnish authorities have declined to comment on identities of the deceased.

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