"As things stand now, 20 member states have offered personnel or material to the so-called European civil protection mechanism" that would coordinate aid to Japan, Van Rompuy said at a joint press conference with Polish Prime Minister Donald Tusk in Warsaw.

"We are also ready to assist in the case the situation in the nuclear power plants deteriorates further," he said, but provided no further details.

Primary assistance would include field hospitals, water purification units, and search and rescue expertise, Van Rompuy said.

"The European Union stands ready to help Japan in whatever way we can," he said, adding that both he and European Commission head Jose Manuel Barroso had contacted Japanese Prime Minister Naoto Kan.

"An earthquake powerful enough to make the Earth wobble on its axis. A massive tsunami, an emergency in nuclear power stations. Any one of these would be a tragedy. Thousands of people have died and this has turned this tragedy into a catastrophe," Van Rompuy added.

Emergency crews continued to work frantically Tuesday to cool reactors at the stricken Fukushima atomic plant on Japan's east coast that emitted dangerous levels of radiation, sparking a health panic as far away as Canada's Pacific Coast.