BEIJING (AFP) - Chinese relatives of passengers on board the missing Malaysia Airlines Flight MH370 gathered under a heavy police presence on Sunday to mark one year since the plane disappeared.

About two-thirds of the 239 people on board the flight were Chinese, but relatives say they have faced harassment from the authorities in their own country as they seek answers on the world's biggest aviation mystery.

Access to the Malaysian embassy was blocked off by dozens of uniformed security, but in the afternoon as police watched, around 30 relatives mounted a small protest in the area, shouting slogans including "Fight to the End" and "Malaysian Government - apologise to us!"

China's ruling Communist Party commonly clamps down on organised gatherings or collective expressions of anger as it seeks to enforce stability.

In the weeks following the plane's disappearance, the relatives of the missing passengers regularly clashed with Malaysian Airlines staff and Kuala Lumpur's diplomats, accusing them of incompetence and deceit.

Some families still hope their loved ones could be alive, clinging to conspiracy theories of hijack and kidnapping.

Earlier on Sunday, about 30 relatives visited the Lama Temple, with around 10 entering the site in groups of two or three to pay their personal respects, as if attempting to keep a low profile.

The remainder waited outside the temple in a group, wearing T-shirts saying "Pray for MH370", and waving placards to photographers reading "Keep searching for MH370".

But most media had been moved on from the area by police, with one officer telling AFP that it was a regulation enforced by the temple.

"The ones wearing the clothes with the words 'Pray for MH370' would find it hard to get in (to the temple)," relatives' leader Steven Wang told AFP.

"We were originally planning to go the embassy or the airport, but I heard there are tonnes of police officers in the two places, especially the embassy. The police have enforced martial law in the area surrounding it," added Mr Wang, whose mother was on the plane.

Chinese foreign minister Wang Yi told a press conference on the sidelines of the National People's Congress, China's Communist-controlled parliament, that the search effort for MH370 would continue.

"Today will be a tough day for the next of kin of passengers on board the flight, our hearts are with you," he said, telling the relatives Beijing would "help safeguard your legitimate and lawful requests and interests".

After waiting for about 90 minutes outside the temple, the relatives walked away to a nearby restaurant, under the close watch of the police.