LHASA, July 20 -- Foreign trade volume in southwest China's Tibet Autonomous Region dropped by 35.09 percent year on year to 3.34 billion yuan (about 545.7 million U.S. dollars) in the first half of 2015 due to a devastating earthquake in April, Lhasa customs announced Monday.

The trade decline was attributed to an earthquake on April 25, which brought Tibet's exports to Nepal to a standstill in May and June.

Nepal has been Tibet's top trading partner since 2006. The bilateral trade between the two sides reached 12.2 billion yuan in 2014, accounting for 88.16 percent of Tibet's foreign trade.

So far, trade at ports on the China-Nepal border has not recovered.

Tibet's trade to Nepal was delayed as roads in Nepal were badly damaged in the earthquake and the upcoming rainy season will make the repairs more difficult, said Li Gang, head of the customs in Nyalam, a major customs center that borders Nepal.

The 8.1-magnitude earthquake which struck Nepal on April 25 and ensuing aftershocks have left nearly 9,000 people dead and destroyed or damaged tens of thousands of houses in Nepal. The China-Nepal Highway and two major ports on the China-Nepal border were severely damaged in the quake.