China has been trying to improve miners' safety
In the biggest blast, which was reported to have taken place on Monday night, at least 24 people died and 40 people were injured in a mine in Jixi city, in Heilongjiang province.
Seven miners were killed in an later explosion at another mine.
Chinese pits have an appalling safety record, with more than 5,600 workers losing their lives in accidents last year.
According to a top safety official, nearly 1,000 people were killed in just the first three months of this year.
Shutting down
On Wednesday, China pledged to cut mining deaths by 10%, and announced plans to close 8,000 small coal mines as part of efforts to streamline and regulate the industry.
More than 12,000 mines have closed because of safety concerns since last May.
The new closures will leave China with about 15,000 mines, down from 82,000 in 1997.
The official China Daily newspaper has highlighted the fact that more than $240m (two billion Yuan) - has been invested in safety equipment and safety measures at hundreds of state-owned coal mines since last year.
The government has also recently promised to invest another $700m in such facilities.
According to Zhang Baoming, head of China's Work Safety Administration, 994 people died in mining accidents between January and March this year - a 13% increase on the same period a year earlier.
And independent analysts believe the yearly death toll may be far higher than the official figures.
They say that the government's pledge to jail officials held responsible for mining accidents may actually lead to more such accidents going unreported.
Several Chinese provinces last year ordered a temporary halt to production in all coal mines, in order to allow safety inspections.
But private mine operators have frequently defied closure orders and continued to operate - or reopened - sometimes with the collusion of local officials.