Hopes were fading Monday for the remaining seven Chinese miners still missing after a deadly gas leak over the weekend that left 30 dead.

The State Administration of Work Safety announced on its website that as of 6 a.m., rescuers had found another four bodies, raising the death toll to 30. More than 200 men had escaped after the Saturday morning leak at the mine owned by the Pingyu Coal & Electric Co. Ltd in Yuzhou city in central Henan province.

Police tightened security around the mine, with dozens of officers blocking entry points and forcing reporters to leave the area. Grieving family members and friends, who had crowded around the mine entrance a day earlier asking for information were nowhere to be seen.

China's mines are the deadliest in the world, with more than 2,600 people killed in coal mine accidents in 2009 alone. The country's lax safety rules and enormous demand for coal to power its economy have contributed to high casualties.

An initial investigation found that 6 million cubic feet (173,500 cubic meters) of gas rushed out, the official Xinhua News Agency reported earlier. The gas leak generated enough force to throw 2,500 tons of coal dust into the mine pit, it said.

The gas wasn't specified, but methane is a common cause of mine blasts. In this incident, there was no explosion but mine safety officials said they were afraid the missing men may have suffocated and been buried by coal dust.

Another gas leak in 2008 at the same mine killed 23 people.

The Saturday accident occurred after Chile's dramatic rescue last week of 33 miners trapped for more than two months underground. Chinese media had very detailed coverage on the Chilean rescue, but information has been very limited on the Chinese mining accident.

Mining deaths have decreased in recent years as China closed many illegal mines or absorbed them into state-owned companies, although deaths jumped in the first half of this year.