The Boeing 777 carrying 239 people disappeared from radar screens on March 8, 2014 while en route from Kuala Lumpur to Beijing.

Two-thirds of the passengers were Chinese, while the others were from Malaysia, Indonesia, Australia, and elsewhere.

Despite the largest search in aviation history, the plane has never been found.

But Malaysian Transport Minister Anthony Loke last month announced that maritime exploration firm Ocean Infinity had resumed the hunt for the missing plane.

Family members said they had been in the dark about the new search.

"It was promised that we would be informed immediately (but) we can only find out about this kind of news online," 68-year-old Li Eryou told AFP before meeting representatives from China's transport and foreign ministries.

"Many families don't even know how to access this information, so they are completely unaware," said Li, who lost his 29-year-old son on the plane.

"We all feel extremely angry and frustrated," Li said.

Jiang Hui, whose mother was on the plane, said that he was still in the dark about the new search.

"When will it start? Where will the search take place? How long will it last? What discoveries have been made? What theories led to the decision to restart the search?" Jiang told reporters.

He hoped the search will "bring an end to the 11 years of suffering".

- 'Trapped in pain' -

The grieving families also gathered Saturday at an intersection in front of the Malaysian embassy in Beijing, the road to which was sealed off by at least 20 police officers.

The attendees shouted in unison "Give us back our loved ones!"

Some held placards asking "When will the 11 years of waiting and torment end?"

Police presence was particularly heavy in the area with officers shooing journalists away and warning them to stop taking photographs of the demonstration.

The plane's disappearance has long been the subject of theories -- ranging from the credible to outlandish -- including that veteran pilot Zaharie Ahmad Shah had gone rogue.

A final report into the tragedy released in 2018 pointed to failings by air traffic control and said the course of the plane was changed manually.

Cheng Liping hoped that China would be able to communicate more with Malaysia to uncover the truth.

"Everyone has been left trapped in pain. What exactly happened is still unknown," said Cheng, whose husband had been in Malaysia for a film shoot and was returning to China on MH370.

When asked what she would tell her husband if given the chance, Cheng, a mother of two boys, said there was "so much I want to say."

"I just hope that no matter where you are, you are healthy, and that we can reunite soon."