Oxfam New Zealand's Executive Director Barry Coates said those contributions were not enough to stop the crisis escalating.
"The humanitarian crisis in the Horn of Africa is at the tipping point.
"Hundreds of thousands will face starvation unless donors step forward, maintain the generosity we have seen in recent weeks and help prevent a catastrophe."
Mr McCully said the Government was continually assessing the crisis and would consider contributing more aid if it worsened.
A spokesman for the minister said New Zealand's aid contributions measured well against other countries when compared to population.
UN figures show about $1.26 billion in aid has been given to address the Horn of Africa drought crisis. But a further $1.4 billion was still needed.
Oxfam New Zealand worker Janna Hamilton saw the far reaching effects of the drought first hand when she arrived in the town of Dadaab-Kenya this week.
"It's hard to comprehend the scale of this crisis," she said. "The rows of tents just stretch on for kilometres and up to 1500 people continue to arrive each day. There's certainly no short fix to this crisis."
Oxfam New Zealand just lifted its fundraising goal for the Horn of Africa to $500,000.
Donations can be made at www.oxfam.org.nz/hornofafrica or by calling 0800 400 666.
INTERACTIVE MAP: IMPACT OF SPIRALLING FOOD PRICES