This just came up a little while ago. I've seen a number of blogs which have complained that foreign countries haven't responded with offers of aid as a result of the devastation of Hurricane Katrina. While I don't know what the case is with other nations, I do know that there is an official Canadian response as stated by Deputy Prime Minister Anne McLellan and Health and Human Services Minister Ujjal Dosanjh. The pertinent material is as follows:
The Deputy Prime Minister added that she has contacted U.S. Homeland Security Secretary Michael Chertoff and advised him that Canada stands ready to provide assistance if needed. In addition, the Minister of Health, Ujjal Dosanjh, has directed the Public Health Agency of Canada to contact the U.S. Department of Health and Human Services and offer any assistance that may be helpful, such as emergency medical supplies contained in the National Emergency Stockpile System.
The important part is that the offer has in fact been made but that official government aid will not be sent unless it is requested.