A Malaysia Airlines official defended the company against criticism that its response had been sluggish and opaque, saying it had brought in a team of nearly 100 people and that relatives would be flown to Malaysia if they wanted to be closer to the search-and-rescue operation.
The first family members are expected to leave Beijing early Monday for Kuala Lumpur, as fears intensified over the fate of those missing, in what would be China's second-worst air disaster.
More than 24 hours after the airplane vanished from radar screens, it was the top topic on Sina Weibo, a Chinese equivalent of Twitter.
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 the worst global air disaster 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."
Some Chinese social media users speculated that the plane could have been hijacked, noting that the incident came a week after a brutal knife attack in the southwest city of Kunming that both Beijing and Washington have described as an act of terror.
"What on earth is happening to China in 2014?" wrote one Sina Weibo user. "First there's the Kunming incident, then a disappearing aircraft. Was it directed at Chinese people? I'm beginning to think more and more that this is terrorism."
The Chinese passengers included a group of artists who had taken part in a painting and calligraphy exhibition in Kuala Lumpur, reports say.
Ignatius Ong, a Malaysia Airlines spokesman, said in Beijing that the search was continuing but that the airline had "informed family members to expect the worst, since so far during search-and-rescue we did not find anything".
At a hotel in Beijing friends and relatives of those on board waited for news, many of them looking tired and worried.
The airline's commercial director Hugh Dunleavy confirmed it was offering to take relatives to Malaysia if they wanted to be closer to the search and rescue effort.
One man told reporters as he exited the hotel that he was going to "sort out his passport".
But several family members criticised the airline's handling of the disappearance and a lack of information.
A middle-aged woman who gave her surname as Nan held back tears as a pack of 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 on Saturday afternoon.
"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. We need Malaysia Airlines to release exact news."
Dunleavy defended the Malaysia Airlines' response, noting that the company had dispatched a team of 92 counsellors and staff to help and that "we came here as soon as we could".
"Even as we speak now we have not been able to locate the aircraft, so you can imagine four or five hours into the event you are much less certain of the information," he said.
Some relatives who had been offered the opportunity to travel to Malaysia said the situation was too uncertain for them to decide whether to travel.
"How can I decide whether or not to go to Malaysia?" said one middle-aged man, between anxious puffs on a cigarette. "The plane isn't even found yet."