The search for Flight MH370 and its black box data and voice recorders has reached a critical point and must not ease up, President Xi Jinping said on Monday.

Chinese personnel involved in the Australia-led multinational search will strengthen their efforts and coordination to help find the plane, Xi told members of the People's Liberation Army air force at its base in Beijing.

Xi, who said the plane's disappearance was a very unfortunate incident, received an update on the air force's involvement in the search in the Indian Ocean west of Perth.