The death toll from a gas explosion in a coal mine in China's southwestern Yunnan province has risen to 34, rescue workers said on Sunday, state news agency Xinhua reported.

Initial reports after the underground blast last week said 19 miners had been killed with dozens trapped at Sizhuang Coal Mine, in Shizong county near the city of Qujing in Yunnan province.

Nine miners remained trapped on Sunday morning and hundreds of rescuers were searching for them, Qujing government spokesman Li Jianjun was quoted as saying.

Li said a 181-metre (600-foot) section of the tunnel had yet to be cleared, and he warned that a risk of large amounts of gas underground would hamper the operation.

Xinhua said the mine was operating illegally, having had its licence revoked a year ago. The provincial coal safety supervision bureau ordered the mine to stop production in April.

In a separate incident, Xinhua said seven miners had been trapped underground by flooding in a coal mine in northwest China's Gansu Province.

The provincial production safety administration said the flooding happened in Sigeshan Tongda Coal Mine in Jingtai County. Rescuers were pumping water out of the mine.

China's mines are the deadliest in the world because of lax safety standards and a rush to feed demand from a robust economy.

In 2010, 2,433 people were killed in coal mine accidents in China, although this was an improvement on the toll of 2,631 the previous year.

(Reporting by Nick Edwards; Editing by Robert Birsel)