The International AIDS Society (IAS) offered its condolences to relatives of those on board the flight in a statement on its website.

"The IAS today expresses its sincere sadness at receiving news that a number of colleagues and friends en route to attend the 20th International AIDS Conference ... were on board the Malaysian Airlines MH17 flight that has crashed over Ukraine earlier today," the statement said.

"At this incredibly sad and sensitive time the IAS stands with our international family and sends condolences to the loved ones of those who have been lost to this tragedy."

The 20th International AIDS Conference, which will go ahead as planned, is due begin on Sunday and run until July 25.

It is believed the former president of the International AIDS Society Joep Lange was among those killed in the attack.

There are also reports that members of the World Health Organisation were also on the flight.

The delegates were planning to change to a connecting flight to Melbourne once the plane landed in Kuala Lumpur.

Michel Sidibé, the executive director of UN AIDS, who is already in Melbourne for the conference, tweeted his condolences to the families of the passengers.