By Matthew Green

LONDON, March 2 (Reuters) - British hedge fund billionaire Chris Hohn has launched a campaign to persuade central banks to starve hundreds of planned coal-fired power plants around the world of finance, aiming to block the projects before they can pose a threat to the climate.

Hohn, a big donor to groups working on climate change, set out his concerns in letters to Bank of England Governor Mark Carney, European Central Bank President Christine Lagarde and the chairmen of Barclays, HSBC and Standard Chartered.

"Coal is the single largest source of greenhouse gas emissions globally and the risks of its continued use in the power sector are not being adequately addressed by regulators and the financial system," Hohn said a statement on the website https://ciff.org/news/ciff-calls-leading-banks-and-regulators-end-coal-finance of his Children's Investment Fund Foundation.

The website published the five letters late on Sunday, and a sixth to the Network for Greening the Financial System, a group of regulators pushing for better supervision of the risks posed by climate change. It includes members with a big economic stake in coal, such as Australia, South Korea, Japan and China.

The climate crisis has moved up the investor agenda in the past year as money managers have increasingly taken into account dangers posed by extreme weather.

Investors are also concerned about possible risks to valuations of coal, oil and gas companies if governments decide to start rapidly cutting carbon emissions in line with the 2015 Paris Agreement to combat climate change.

Hohn, founder of hedge fund TCI, has emerged as one of the most outspoken investor voices urging companies to do more to tackle their own carbon emissions, and threatened in December to vote against directors who failed to act.

In his letter to Carney, dated Feb. 28, Hohn warned that British banks were "highly likely" to suffer losses on coal financing as the cost of renewables continued to fall and regulations on air pollution and carbon emissions tighten.

He called for a dramatic tightening of the application of a supervisory requirement known as the "risk-weighting" applied coal loans - a move that would make coal plants far more difficult for banks to finance.

Hohn also urged regulators to force banks to publicly disclose their exposure to coal.

In his letters to Barclays, HSBC and Standard Chartered, Hohn urged the banks to reveal any coal exposure on their balance sheets and classify such loans as high-risk. The banks were not immediately available for comment. (Reporting by Matthew Green; editing by Richard Pullin)