COLOMBO, (Reuters) - Relief has begun to trickle into drought-stricken southern Sri Lanka but the Red Cross said on Friday aid was still far short of what was needed to help the drought’s 1.5 million victims.

Donors have been relatively slow to respond because the effects of the drought appear to be less devastating than expected and because of a spontaneous local relief effort, the International Federation of Red Cross and Red Crescent Societies said.

"We launched an appeal for 77 million rupees ($850,000) and we have received around 18 million so far," said John Gwynn, the federation’s representative in Sri Lanka.

The Sri Lankan government estimates that 1.5 million people across seven of the country’s 25 districts have been affected by the Sri Lanka’s worst drought in half a century.

Gwynn said the drought was not "a full-scale disaster" but there were still pockets of "extreme vulnerability".

Aid agencies said they would need to distribute an estimated 45,000 tonnes of food over the next six months even if rains return soon to the island’s parched southeastern corner.

The drought in the normally lush tropical island was first brought to the world’s attention last month by a Red Cross appeal for international aid.

Local charities and social service groups responded with a spontaneous relief effort that Gwynn said was too poorly coordinated to have much effect.

"I think many donors are waiting for the local response to dry up," he said.

Worst hit is the Hambantota district, one of Sri Lanka’s driest and poorest areas, where the rains have failed for more than 21 months.

Most of its residents are subsistence farmers, and families earn an average monthly income equal to $7.