Millions of dollars in donations and pledges were pouring in to Canadian aid agencies Thursday for disaster relief in earthquake-shattered Haiti - so much that their web servers teetered on the brink of collapse.

The overwhelming response prompted the minister of national revenue to advise Canadians to make sure they donate wisely, and avoid getting scammed.

"Canadians have opened their hearts and their wallets in the wake of the terrible tragedy in Haiti," Jean-Pierre Blackburn said at a news conference on Parliament Hill in Ottawa.

"Sadly, there are some who would exploit the generosity of Canadians."

Blackburn said Canadians who wish to donate should check the Canada Revenue Agency website at www.cra.gc.ca for information on how to be an informed donor.

Kieran Green of the Humanitarian Coalition, which includes Care Canada, Oxfam Canada, Oxfam Quebec and Save the Children, said the donations were "quite literally overwhelming."

"The company that does our online donations has said that they have already had a couple of servers go down from the volume of the response," Green said early Thursday.

"Our phone centres are telling us that the volume of calls is massive," he said.

The servers were soon back up and the coalition was pleading with Canadians to keep trying, because the agencies need the money to help people in the earthquake-shattered country.

Doctors Without Borders reported the same massive response, with spokeswoman Avril Benoit tweeting on Twitter that they were "white-knuckling it" as the agency's website "teeters from overload." The group said it had to hire outside help to keep the server from crashing.

In a telephone interview with The Canadian Press from the earthquake's ground zero, Port-au-Prince, Red Cross worker Miriam Castaneda pleaded for more donations from Canadians.

"We are trying to get the goods that are required, the items that are required for the provision of first aid," said Castaneda, who has been in Haiti with the agency since last September.

"If Canadians can help we are encouraging them to support the Red Cross relief effort by donating cash," she said.

"We need their help and all the assistance they can provide...(for) emergency shelter, food, water and other essentials here."

As of early Thursday afternoon, Canadian Red Cross spokeswoman Katie Kallio said the agency had collected $2.6 million in pledges and donations. About $1 million of that came in within the first 24 hours.

"Canadians are always generous in times of disaster and they're certainly showing their care and compassion once again," Kallio said.

World Vision, which launched social media campaigns on Facebook and Twitter, says the number of donations and pledges were 10 times the usual. It said $1.4 million had been raised since the earthquake hit.

Prime Minister Stephen Harper and his wife Laureen made a donation to the Canadian Red Cross in Ottawa on Thursday afternoon.

By mid-afternoon, The Humanitarian Coalition said $600,000 had been pledged and donated, and the organization expected to reach $1 million by the end of the day. That number did not include separate amounts pledged to the coalition members.

The federal government said it would match any donations made to registered charitable groups for the Haitian disaster from Jan. 12 to Feb. 12, up to a maximum of $50 million.

Despite the outpouring of pledges and donations, the Red Cross's Kallio said such a major disaster would require yet more money to help up to three million Haitians - a third of the country's population - affected by the earthquake.

"It's very important to note the needs on the ground right now are huge, and this outpouring of support will absolutely make a difference in the lives of survivors, but much more is needed," she said.

Other charitable groups launched campaigns as well.

The Canadian Conference of Catholic Bishops and and the Canadian Catholic Organization for Development and Peace, as well as the United Church, donated funds and urged their church members to do the same.

The Salvation Army in Canada sent an immediate $100,000 and began a fundraising campaign.

Ted Menzies, parliamentary secretary to the minister of finance, said "the fastest and most efficient way to get help to people in critical need is to donate money to experienced humanitarian organizations."

"There are many charitable organizations that have personnel and equipment on the ground in Haiti already," he said. "These same organizations can deliver much needed humanitarian aid to that country immediately."

The Department of Foreign Affairs and International Trade has compiled a guide designed to help the public avoid scams and ensure their donations are of maximum value.

It can be found online at www.international.gc.ca.