The death toll in the major coal mine explosion in northeast China's Heilongjiang province has risen to 138 with 11 others still reported missing, rescuers said on Monday.

Rescuers found four more bodies killed in Sunday's blast at Dongfeng Coal Mine run by the Qitaihe branch of the Longmei Mining (Group) Co Ltd in Heilongjiang Province.

There have been reports that investigators are finding it difficult to know the exact number of miners involved in the accident as the attendance roll showed that there should be 254 miners. However, the number of miners' lamps showed that 221 actually went into the coal pit.

Altogether 221 miners were working underground when the blast went off on Sunday night at the coal mine of which only 72 miners escaped the explosion site.

Efforts are on to trace the remaining 11 miners missing after the explosion.

Investigators said the tragedy was caused by coal-dust explosion, which knocked out all ventilation systems in the pit.

The blast was the latest disaster to strike Heilongjiang, whose capital city, Harbin, had to suspend water supplies for five days due to a serious toxic spill contaminating the Songhua River, the main source of water supply to nearly four million people.

China, the world's largest coal producer, has witnessed a series of major coal mine accidents this year as the nation faced an acute power shortage.