Internal state government and corporate documents, cited by The Australian, show Anglo American's Grosvenor underground mine was plagued by "high-potential incidents" ahead of the fatalities in May.

The documents also show the government's mines inspectorate repeatedly visited the underground site but never ordered Anglo to suspend operations.

The documents show that in 2016 and 2017 the mine had a series of rock fractures that released uncontrolled levels of methane.

Those incidents sparked investigations and in October 2017 Anglo was warned methane monitors might not be providing true readings and that undetected explosive levels of methane could be present, The Australian reported on Monday.

Inspectors told Anglo that Grosvenor, as a single mine, was responsible for 60 per cent of all methane exceedances in the state's nine underground mines.

In May 2018, Anglo was finally warned the mine's continued methane "high-potential incidents" was unsatisfactory and must be minimised or eliminated.

But there were at least 31 more high-methane incidents between then and the explosion on May 6 this year, which left five workers fighting for life. Four of them are still in hospital while the fifth has been released.

An Anglo American spokeswoman told The Australian many of the high-methane incidents were picked up by the mine's extra sensors.

A spokesman for the Queensland Mines Inspectorate would not say why Grosvenor wasn't ordered to suspend mining in response to the incidents.

An independent inquiry will determine what caused the explosion. The state government is expecting an interim report in August.

Australian Associated Press