A prominent researcher, two activists and at least three others headed to an AIDS conference in Australia were among those killed when a Malaysian passenger jet crashed in Ukraine after being allegedly shot down.

Among the passengers was Joep Lange, who researched the condition for more than 30 years and was considered a giant in the field, admired for his tireless advocacy for access to affordable AIDS drugs for HIV positive patients living in poor countries.

"He's one of the icons of the whole area of research. His loss is massive," Richard Boyd, professor of immunology at Monash University in Melbourne, told Reuters.

Earlier reports had sad as many as 100 people heading to the AIDS 2014 conference in Melbourne were on the doomed flight.

"The cure for AIDS may have been on that plane, we just don't know," Trevor Stratton, an AIDS consultant who was attending a pre-event in Sydney, told the ABC network as the news were initially reported.

"You can't just help but wonder about the kind of expertise on that plane."

Conference to go ahead

The conference, due to start on Sunday is expecting about 12,000 participants.

"In recognition of our colleagues' dedication to the fight against HIV/AIDS, the conference will go ahead as planned and will include opportunities to reflect and remember those we have lost," a spokesman said.

Peers paid tribute to Lange, a Dutch professor of medicine at the Academic Medical Centre at the University of Amsterdam.

The Malaysian Airlines Boeing 777 was en route from Amsterdam to Kuala Lumpur when it was allegedly shot down on Thursday by a surface-to-air missile in an area of eastern Ukraine where Moscow-backed rebels have been fighting government forces.

Lange pioneered access to key AIDS medicines in poor countries, including combination drugs to control HIV and antiretroviral medicines to prevent transmission of the virus from mothers to their babies.

The World Health Organisation said its media spokesman Glenn Thomas was also among those on board Flight MH17.

Gregory Hartl, a WHO spokesman, said in Geneva that Thomas had been with the organisation for more than a decade.

"Glenn will be remembered for his ready laugh and passion for public health," he said.

"He will be greatly missed by those who had the opportunity to know him and work with him. He leaves behind his partner Claudio and his twin sister Tracey."