CUBADAK AIR, Indonesia (AlertNet) - Persistent rain and poor sanitation threaten to speed up the spread of disease among thousands of homeless survivors of a devastating earthquake in Indonesia.

In Padang, the biggest city in the earthquake zone, the authorities have erected tents for the homeless and are handing out medical supplies and fresh water, but in outlying villages like Cubadak Air help has only just started trickling in.

"We can't live like this, I'm scared. When it rains it leaks through the sheet," said 50-year-old Masniati. Her home now was a sheet of plastic attached to the side of a ruined building that had been her house until the earthquake hit five days ago.

"We need food, water and proper shelter."

Masniati's brother-in-law had been injured in the earthquake and lay in the nearby medical centre unable to move.

There were seven other people living in the makeshift shelter with Masniati. They have no clean water and only enough food for another two days. They wash their clothes in a nearby muddy, brown stream.

A local official said the earthquake had damaged all 200 houses in the village and that none are now fit to live in.

Time is running out to get help to people stranded in remote areas - many cut off by landslides - said Malka Older, director of programmes at the aid group Mercy Corps.

"What we're seeing is an urgent need for clean water," she told AlertNet. "People are sleeping outside and there are real worries that people outside Padang city are already coming down with malaria."

She added that the survivors were becoming increasingly desperate.

"We heard that people are drinking water out of drains," she said.

Indonesia's health minister has estimated that the final death toll from the earthquake could reach 3,000, adding that disease was becoming a concern.

Investigators have already said too many of the buildings in the area were poorly constructed and the mayor of Padang has promised to push through a law to ensure that every new building can withstand a strong earthquake.

But for now the people of Chubadak Air and other villages in the earthquake zone are still stunned by the devastation.

"When the earthquake hit I was so scared that I couldn't move at first. I thought I would have a heart attack," Masniati said.

Zainyar, a 73-year-old woman wearing a pink and white traditional outfit, was sitting nearby.

"We always have earthquakes here but they are only small ones. This one was very big and dangerous," she said. "I had to hug a tree to survive."

(Writing by James Kilner in London)

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