Anglo American PLC told senior staff at its Grosvenor metallurgical coal mine in Queensland, Australia, that a second blast may have occurred at the site on June 8, The Australian reported July 1.
No injuries were reported as all workers had been evacuated about an hour before the second explosion, according to the report.
The Queensland Mines Inspectorate also confirmed that the mining giant had notified it of the possible methane explosion at Grosvenor.
The incident is under investigation by the inspectorate, and the Queensland Coal Mining Board of Inquiry may also start a probe into the initial blast in May, which injured five people and forced operations to shut down.
An Anglo American spokeswoman said the incident could not be confirmed as no one had visited the underground area since the explosion.
"We made the decision to withdraw personnel from the underground environment last month in line with our risk management processes, and have been working with our expert technical advisers to respond to the situation," the spokeswoman said.
The Australian recently reported that Australia's Queensland government was informed of the recurring "high-potential incidents" of dangerously high methane levels at the Grosvenor mine.