The Group of Seven rich nations will discuss on Thursday possible steps to calm volatile financial markets roiled by fears about the deepening crisis in Japan.

The yen hit a record high against the dollar on Wednesday on expectations that Japanese investors will bring home cash from abroad to help finance reconstruction.

A G7 source told Reuters that G7 finance ministers and top central bankers would hold a conference call late on March 17. The source provided no further details.

A French government source said earlier on Wednesday that the telephone talks would take place before the weekend.

In a sign of the degree of concern among top policymakers, one G7 central banker, who asked not to be identified, said he was extremely worried about the wider effects of the crisis in Japan, the world's third largest economy.

I think the world economy is going to go right down and it has happened at a time when financial markets are still very fragile, he said.

G7 officials will address the impact of the crisis on economic growth, energy output and the supply chain, plus its effect on volatile markets, the French government source said.

Friday's devastating earthquake, tsunami and a subsequent nuclear crisis have wiped hundreds of billions of dollars off global stock markets.

The dollar fell more than 4 percent against the yen to as low as 76.25 yen on trading platform EBS, breaching a previous record low of 79.75 set on April 19, 1995.

Apart from intervention, there isn't much to stop this slide, and the dollar doesn't look like it's coming back soon, said Brian Dolan, chief strategist at Forex.com in Bedminster, New Jersey.

A prolonged surge in the value of the yen could hinder Japan's recovery from the disaster by making it harder for its export-focused companies to sell goods abroad.

Japan's damages from the crisis, in terms of destruction and lost output, remain hard to gauge but economists estimate it could cost Japan up to $200 billion.

Japan is a major contributor of technology components and capital goods to the regional supply chain, and major disruptions could have a ripple effect across Asia.

We need to be at the disposal of our Japanese friends on monetary matters, said French Finance Minister Christine Lagarde, who chairs meetings of G8 and G20 finance ministers this year.

I have asked for a meeting of G7 finance ministers and central bankers so that we can see in what way we can take part in their debt issues and how we can react on a financial level, Lagarde told reporters after a weekly cabinet meeting.

G7 ministers will use this week's call to ask for an update from Japan's finance minister on the impact of the earthquake and tsunami before moving on to specific issues like the volatility in financial markets, the French source said.

European Central Bank Governing Council Member Christian Noyer, who is also governor of the Bank of France, said the ECB would weigh the impact of the crisis on its policy decisions, though analysts said this did not dilute expectations of an ECB interest rate rise in April.

Nuclear power accounts for 30 percent of Japan's energy and prolonged disruption would mean it would need to replace much of it with other sources like fossil fuels, driving up prices.

German Finance Minister Wolfgang Schaeuble said a meeting of G20 finance ministers and central bankers next week in China, supposed to discuss reform of the global monetary system, would be an opportunity to discuss Japan.

The necessary and the possible will be done, Schaeuble told a news conference in Berlin, adding it was too early to talk about how the international community might aid Japan.

(Additional reporting by Emmanuel Jarry and Leigh Thomas in Paris, Gernot Heller in Berlin and Wanfeng Zhou in New York; Writing by Daniel Flynn; Editing by Catherine Evans and Leslie Adler)

Japan