Image copyright AP Image caption Screens at Noi Bai Airport in Hanoi broadcast unscheduled messages on Friday

Flight display screens at Vietnam's two largest airports were hacked to show messages criticising Vietnam's claims of territory in the South China Sea.

China's territorial claims, which overlap with Vietnam's, were recently rejected by an international tribunal.

Screens and sound systems at Hanoi and Ho Chi Minh City airports broadcast anti-Vietnamese and Philippines slogans on Friday.

Vietnam's transport ministry said a Chinese hacker was responsible.

Vietnam Airlines' website was also briefly hacked.

Media in Vietnam reported that staff at the airports had to resort to checking in passengers manually, avoiding computers for several hours.

The hack comes days after a row involving a Chinese tourist at one of the hacked airports - Tan Son Nhat, in Ho Chi Minh City.

China asked Vietnam to investigate reports that a Chinese visitor's passport was handed back with obscenities written on two pages.

Pictures show a four-letter word written on the pages that contain a map including China's "nine-dash line", that marks China's claim to territories in the South China Sea.

Image copyright People's Daily

The tourist, surnamed Zhong and from China's Guangdong province, was entering Vietnam through Tan Son Nhat airport.

She told local media that she was "very disappointed at the personal qualities of Vietnamese officials".

The Chinese consulate in Ho Chi Minh City said in a statement the act was "shameless and cowardly", adding that it had "stained the dignity of both China and its nationals".

New passports were issued by Beijing in 2012 with revised maps to include the "nine-dash line".

China claims almost all of the South China Sea, including reefs and islands that are also claimed by other countries, and has controversially been engaging in island-building and naval patrols.

It has said it does not recognise an international tribunal ruling in July that said its claims had no legal basis.

Customs officers at Vietnam's Da Nang airport, not one of those hacked on Friday, have reportedly also confiscated maps featuring the nine-dash line from Chinese passengers.

A provincial Vietnamese television station stopped airing Shanghai Bund, a Chinese remake of a Hong Kong series, after the show's lead actor voiced his support for Beijing's claims in the South China Sea.

About 20 people were also detained in Hanoi in July while protesting against China's rejection of the tribunal decision.