VANCOUVER - A Canadian group that sends medical teams to disaster zones returned home Wednesday from a short-lived trip to Japan, forced to turn back in the face of the worsening crisis at a nuclear power plant damaged in last week's deadly earthquake and tsunami.

The Ontario-based Canadian Medical Assistance Team sent six paramedics and one search-and-rescue expert to conduct an assessment of what's needed and inform authorities in Japan what they could offer, said spokeswoman Valerie Rzepka.

The group left for Japan on Sunday, but arrived back in Canada within days due to the escalating problems at the Fukushima Dai-ichi nuclear plant in the country's northeast. The team wasn't equipped to deal with a nuclear emergency, said Rzepka.

They plan to co-ordinate their potential response from Vancouver.

The team, known as CMAT, is one of the many relief groups and non-governmental organizations heading to the region to offer help, along with governments that have sent supplies and relief personnel, including Canada.

But despite the desire to help stricken Japan, one expert cautioned that non-governmental organizations, especially smaller groups that don't have the resources and experience of bodies such as the Red Cross, risk being ineffective or worse if they arrive in disaster zones unannounced.

Rzepka said the medical assistance team went on their own accord, and planned to assess the situation for themselves to determine what might be required for a larger deployment.

The group is registered with the United Nations Office for the Co-ordination of Humanitarian Aid, said Rzepka, and would only send a full team if they received a request through the UN's electronic disaster co-ordination system.

Rzepka said her group is well aware of the potential problems that can occur when relief groups enter a crisis ill-prepared and unorganized.

"When our teams are deployed, we supply them with ready-to-eat meals, with water purification systems, with tents, so we do not become a burden on the local community, because they have enough to cope with on their own," she said.

Rzepka said her group typically sends an assessment team into disaster zones immediately to ensure they are ready if they are called upon to respond.

"The Japanese authorities have absolute control over the response, and we respect that," she said.

"Once that request is made, rather than scrambling to get it together, we have the assessment in place, we know what to send."

Nipa Banerjee, an international development professor at the University of Ottawa, said NGOs should be cautious about entering a disaster zone on their own and without the co-ordination of a larger body such as the UN.

Banerjee, who worked for the Canadian International Development Agency for 30 years, said small self-styled humanitarian groups often flood into disaster areas too quickly, and that can leave them ineffective.

She said such groups run into problems if they don't know the local language or how to get around in an unfamiliar and sometimes-chaotic country.

"I personally don't think that as soon as there is an emergency, NGOs should land there," Banerjee said in an interview.

"Without knowledge of the country and the situation, it is very difficult for them to be effective. And they become more of a problem because the government itself has to take care of their security sometimes, their food, their lodging, all those sorts of things."

Banerjee praised the work of Oxfam, CARE and the Red Cross, and said NGOs are essential in emergency situations -- if they're invited.

But she said when she was at CIDA, the federal agency had a policy not to fund any NGO work unless the UN had issued an appeal for help.

Officials with CIDA and the federal Foreign Affairs department could not be reached for comment.

Bas Brusche of the Canadian Red Cross said local Red Cross organizations already have standing agreements with local governments about their responsibility should a disaster strike.

The Japanese arm of the Red Cross went into action immediately, said Brusche. Other Red Cross societies, including Canada's, are sending money collected through donations, but they won't send volunteers or supplies until they're asked.

"We work through the Japanese Red Cross, and whatever we do as the Canadian Red Cross is built on that, we support the Japanese efforts already on the ground," he said.

"The international Red Cross societies will get involved upon request of the national society. It sounds bureaucratic, but it is essential to work like that, because we have to enforce what is already there."

So far, Canadians have donated $6 million toward the Red Cross relief effort in Japan, said Brusche.