Cate Blanchett has added to her list of worthy causes, with the release of a video calling for support for refugees fleeing to Europe to escape the armed conflict in Syria.

In the video put on YouTube on Thursday, the two-time Oscar winner explains why she was motivated to support the United Nations' refugee agency.

"I'm supporting the UNHCR's appeal for the refugee crisis in Europe," a bespectacled Blanchett says directly to the camera.

She explains how she met a Syrian woman in Lebanon who was an architect, with "no reason at all to leave Syria except to run, to run from war with her children, leaving everything behind".

"As a mother I can only imagine the difficulty and distress of making such a decision,'' says Blanchett, a mother of four.

In the video, which runs for just over a minute, Blanchett and husband Andrew Upton are pictured in Lebanon.

The couple travelled to the Middle Eastern country, which hosts more than 1 million refugees from Syria, earlier this year to "further understand the Syrian crisis", according to UNHCR spokesman Greg Mills.

A video of her experience in Lebanon was uploaded to YouTube for World Refugee Day in June.

Blanchett's previous social activism includes being photographed with a poster in support of Indigenous AFL player Adam Goodes and promoting the carbon tax in 2011 – a campaign that led her to be labelled 'Carbon Cate'.

Images of distressed children in lifejackets being rescued form an overcrowded vessel are shown as Blanchett says the Syrian woman told her she had "no option left to her but to make the dangerous sea passage to Europe".

"I think of Halud often and hope that she and her children are receiving the care and support they so desperately need as refugees," Blanchett says.

Blanchett points out there are thousands of other families in Europe suffering the same plight.

Blanchett concludes by calling on people to support the UNHCR: "I have seen the UNHCR's work firsthand and I know that work makes a difference.''

Blanchett is currently performing in the Sydney Theatre Company's production of Chekhov's first play The Present.