Exact number of dead and missing from Monday’s dam collapse remains a mystery because of rescue operation’s complexity.

Rescuers battled thick mud and floodwaters across a swathe of remote southern Laos to find survivors of a dam burst that submerged entire villages, as an official suggested more than 1,100 people may still be unaccounted for.

Two more bodies were found on Saturday, bringing the total death toll to at least 29. Heavy rain and thick mud hampered the operation.

“It is impossible for many areas to be reached with vehicles or even boats,” Laos’ Disaster Management Committee said in a report published by state media KPL on Saturday.

The exact number of dead and missing from Monday’s dam collapse remains a mystery because of the complexity of the rescue operation in an inaccessible area, and the secretive reflexes of Laos’ communist authorities in the face of the unprecedented crisis.

“The search is very complicated, many areas cannot be accessed by cars or boats. Also we have limited modern equipment to bring to the field,” deputy secretary of Attapeu province committee Meenaporn Chaichompoo told reporters Friday.

She said hundreds still have not been located, five days after the dam burst.

“We can’t find 1,126 people,” she said, adding 131 have been confirmed missing by relatives.

‘Treacherous search’

The remoteness of the disaster zone and slow trickle of often contradictory information has sparked fears the death toll could rise sharply.

A stretch of land dozens of kilometres long and wide was submerged when the Xe-Namnoy dam collapsed after heavy rains.

Slowly retreating floodwaters have cut off access to villages and covered much of the area with thick, sticky mud.

Days into the treacherous search for survivors, questions are being raised about the quality of the construction of the $1.2bn dam, a joint venture between South Korean, Laotian and Thai firms.

Operators said it burst after heavy rains in a country regularly battered by monsoons.

Laos has a total of 46 hydroelectric dams with many more planned. Its power export accounted for up to two-thirds of its total exports, according to the International Hydropower Association.