VILNIUS (Reuters) - From the Ukrainian frontline to the Pacific islands of Vanuatu, hundreds of thousands of Lithuanians simultaneously sang their national anthem on Saturday in an annual demonstration of unity.

The tradition, launched in 2009 to mark 1,000 years of history, unites the Central European nation of 2.9 million with its diaspora, estimated in hundreds of thousands.

Almost half of Lithuanians sang in 2009 in at least 56 places around the world, a Nordstat poll showed. It has since been repeated annually on July 6, at 9 p.m. Vilnius time (1800 GMT).

Raimundas Daubaras, who organised the first event in 2009, said he got the idea after hearing emigrees in Australia sing the song: "They sing the Lithuanian anthem very differently. For them, it's about keeping the connection alive."

In Vilnius on Saturday, over 65,000 people sang "Lithuania, our homeland, land of worthy heroes..." in an open-air square, as part of the final concert of a national song and dance festival.

In videos posted online, the anthem was sung by Lithuanian volunteers in the Ukrainian army at the frontline, endurance divers singing under a lake, and climbers in Georgia on the summit of Kazbegi, the second highest mountain in Caucasus.

Eimantas Kazlauskas, who has lived on the tiny Pacific Island nation of Vanuatu for the past six years, told Reuters in an email he had sung it under the Lithuanian flag, which locals had noted bears the same yellow-green-red colours as their own.

"Doing this, we feel that we are closer to our country, our families, our ancestors which fought for its independence," he said.

(Reporting by Andrius Sytas in Vilnius; Editing by Peter Graff)

By Andrius Sytas