Aid has been sent to the Indian Ocean region from across the world

The Disasters Emergency Committee has predicted the UK will raise �200m.

Debra Allcock-Tyler, from the Directory of Social Change (DSC), which advises many charities, said some organisations could feel the impact.

And Cancer Research Wales is urging people to remember that their money is still needed for other causes.

Ms Allcock-Tyler, chief executive of the DSC, which gives information and training to the voluntary sector, said charities needed to take measures "to protect their long-term future".

It is sensible for charities to be thinking about it and be prepared for receiving less Cathy Pharoah, Charities Aid Foundation

"Many charities survive day-to-day, and are often not able to think ahead," she said.

"It would be a real pity if a charity doing important work found itself unable to carry on because of bad planning."

She urged charities to have contingency plans and consider other sources of income.

Cathy Pharoah, research director at the Charities Aid Foundation which gives specialist financial services to charities and their supporters, agreed there was "a risk some charities would get less money".

She drew a comparison with the response to the terrorist attacks in the United States on 11 September, 2001.

"If you look back at 9/11, altogether about 1% of giving went to that appeal that year," she said.

More than �100m has been raised in the UK so far

She said that after 9/11 the total amount of money given to charities by people in the UK did not rise.

"It is sensible for charities to be thinking about it and be prepared for receiving less, or working harder to get what they normally do," she said.

But Campbell Robb, director of public policy at the National Council for Voluntary Organisations (NCVO), said there was "no evidence to suggest it would have a major effect on other fundraising activities within the charity sector".

"Many donors give on a regular basis to their favourite good causes and are likely to be digging even deeper than usual in order to support the victims of the tsunami," he said.

"NCVO hopes that the tsunami appeal will in fact encourage people who do not already give to charity regularly to consider doing so."

Minds focused

Charities said it was too early to predict the impact of tsunami fundraising on them.

But Bob Fawkes, from Cancer Research Wales, urged people that their money was still needed for other causes.

"I think the general view is charities will be expected to suffer," he said.

Catherine Hester, head of Oxfam in Wales, said she hoped the donations given to tsunami victims would actually help increase its relief efforts throughout the year.

Working with nearly 100 other charities, Oxfam is taking part in the Make Poverty History campaign for 2005.

"The tsunami has focused people's minds on the issue," said Ms Hester.

"We want people to keep that focus, keep that momentum going and look at the wider space."