KATHMANDU, Oct 9, 2008 (AFP) - Poor visibility caused the crash at a tiny airstrip in Nepal's Mount Everest region that killed 18 people, including 12 German tourists, officials said Thursday.

The Yeti Airlines Twin Otter plane flying from the capital Kathmandu crashed and burst into flames Wednesday morning at an airstrip in eastern Nepal, killing 12 Germans, two Australians and four Nepalese.

'The plane crash was due to poor visibility,' Mohan Adhikari, a senior airport official, told AFP.

The airport is the gateway to Nepal's Everest region and used by thousands of trekkers and mountaineers each year to access the stunning Himalayan range that forms Nepal's northern border with Chinese-controlled Tibet.

The weather at the airport in Lukla, 140 kilometres (90 miles) northeast of Kathmandu, changes frequently and swiftly.

Pilots are supposed to have five kilometres (three miles) of visibility to land at the 550 metre-long (1,815 foot) sloping airstrip perched on a hillside 2,757 metres above sea level, Adhikari said.

'When the flight left Kathmandu, they had five kilometres of visibility at Lukla, but by the time they arrived after 40 minutes of flying, visibility suddenly worsened,' said Adhikari.

'Two planes had already landed that morning so the pilot (of the plane that crashed) must have thought he could too,' he said.

The plane slammed into the hillside and burst into flames around 50 metres short of the runway at the small Tenzing-Hillary Airport, named after Everest pioneers Sir Edmund Hillary and Tenzing Norgay.

'When the aeroplane was on its final approach, suddenly fog and heavy mist came up from the valley below. The plane descended and disappeared inside the thick mist and very shortly afterward we heard a big bang,' said Suraj Kunwar, a journalist for Nepal media group Kantipur who witnessed the crash.

The bodies of those killed in the crash were transported to the capital on an army helicopter Thursday and were in a hospital morgue awaiting identification, officials said.

The pilot, who was the lone survivor, was recovering from his injuries and would be interviewed as part of a probe by Nepal's government, Adhikari said.