Relatives were taken to a hotel near Beijing airport, put in a room and told to wait for information from the airline, but none came. Malaysia Airlines said at least 152 of the 227 passengers on flight MH370 were Chinese.
About 20 people stormed out of the room at one point, enraged they had been given no information.
"There's no one from the company here, we can't find a single person. They've just shut us in this room and told us to wait," said one middle-aged man, who declined to give his name.
"We want someone to show their face. They haven't even given us the passenger list," he said.
Another relative, trying to evade a throng of reporters, muttered: "They're treating us worse than dogs."
Amid chaotic scenes, an unidentified Malaysia Airlines official spoke to reporters for just a few minutes without taking questions before leaving.
"We are working with authorities who have activated the search and rescue teams," the official said. "Our thoughts and prayers are deeply with the affected passengers and their family members."
Adding to the confusion, the official mentioned a rumour that the Chinese government has already denied - that the aircraft had landed in the southern Chinese city of Nanning.
"There has been speculation that the aircraft has landed in Nanning. We are working to verify the authenticity of the report of others," the official said.
Some Chinese media reported that he meant a place in Vietnam called Nanming. It was unclear exactly what he was talking about.
Chinese media outlets took to their official Weibo microblogs to criticise the airline for taking so long to announce what was going on and for refusing to answer questions.
"Malaysia Airlines, why did you wait for five hours after losing contact with the aircraft to first announce the news, and why did you only have a news conference after almost 13 hours" the official Xinhua news agency wrote on one of its Weibo accounts.
Sanved Kolekar, an Indian working in Beijing, stood stunned at the airport where he was waiting for his parents who were coming over on a visit.
"My parents are on the flight, they were supposed to come here at 6.30, I don't know what happened," he said. "They haven't given me any information, it's very difficult because I don't understand the local language."
Malaysia Airlines told passengers' next of kin to come to Kuala Lumpur's international airport with their passports to prepare to fly to the crash site, which has still not been identified.
About 20-30 families were being kept in a holding room at the airport, where they were being guarded by security officials and kept away from reporters.
Malaysia Airlines said people from at least 14 nationalities were among the 227 passengers.
Chinese media said at least 24 artists and their family members were aboard, returning from an art exchange forum, including a well-known calligrapher.
At least two names on a passenger list released by Beijing police appeared to have been redacted, with the names pixillated out, leading to online speculation that they could have been ethnic Uighurs, a Muslim people from the restive far western Chinese region of Xinjiang.
The government has not confirmed this, and it was not possible to reach Beijing police for comment.