Aviation experts map out possible causes of Malaysia Airlines crash.
Friends and family of two Queensland couples on the missing China-bound Malaysia Airlines jet are praying for a miracle.
Catherine and Robert Lawton, from Springfield Lakes, and friends Mary and Rodney Burrows, from Middle Park, are among 239 people on board Flight MH370.
Two other Australians on the flight, Li Yuan and Gu Naijun, are from Sydney.
The Lawtons are described as passionate travellers who dote on their three daughters and two grandchildren.
"Bobby's a very good father, such a good person," Robert Lawton's brother David Lawton told News Corp.
His wife Rhonda said the couple, in their mid-50s, had planned the trip to China with their good friends the Burrows.
"Cathy's last comment on Facebook was 'Off to China'," she said.
In Middle Park, neighbours Mandy Watt and Don Stokes said the Burrows were hard-working parents of two adult daughters and a son, and had downsized just a fortnight ago.
"The kids had moved on ... they're all successful, all happy. This was their time," Watt said.
"I hate to use the cliche but they were soulmates."
Stokes said Rodney Burrows planned the overseas trip after being made redundant last year.
Australians used social media sites to express hope for all the passengers' survival. "Praying for a miracle," one person wrote.
The families of missing Chinese passengers and web users across the country have expressed fears for their relatives and compatriots on board missing Malaysia Airlines flight MH370.
Yesterday the disappearance was the top topic on Sina Weibo.
According to the airline 153 Chinese citizens were among the passengers on the flight, which was a codeshare with China Southern Airlines.
If the loss of the aircraft is confirmed it would be China's second-worst air disaster, and the worst globally since 2001.
A widely circulated post on China's hugely popular messaging app WeChat read: "MH370, we hope the radar can see you. If you copy, keep flying at your current height until you reach your destination.
"We'll clear the way for you. Everybody is more than happy to let you be the first to land.
"The sky is clear, with temperature in Beijing at five degrees Celsius, a little bit cold. Please wear your coats to keep warm.
"Remember to hug your family and friends after you disembark. They love you, they really do."
The Chinese passengers included a group of artists who had taken part in a painting and calligraphy exhibition in Kuala Lumpur, reports say.
At a hotel in Beijing friends and relatives of those on board waited for news, many of them looking tired and worried. One man told reporters he was going to "sort out his passport" - a sign that some relatives may be planning to travel to Malaysia.
Malaysia Airlines has dispatched teams of counsellors and staff to help, but several family members have criticised its handling of the disappearance and a lack of information.
A middle-aged woman who gave her surname as Nan held back tears as reporters surrounded her.
Her husband's brother was on the flight, returning from a business trip, and she took a train to Beijing from Shanghai after she found out.
"The airline company didn't contact me, it was a friend," she said. "I can't understand the airline company.
"They should have contacted the families first thing. I don't have any news. I'm very worried, my family member was there."
Another middle-aged woman, Peng Keqing, told reporters that her husband's sister, who had been working in Singapore, was on board.
"We've just been waiting," she said. "We arrived last night. We didn't get any direct notice, I checked the information online."
A man surnamed Liu from the city of Tianjin said his son, who has a 7-year-old child, was on a business trip with a colleague.
"He was 33 this year," Liu said. "He has a child. We didn't tell his child. His wife knows, but we didn't let her come to Beijing in case it was too much."
- AFP, AAP