DONKIN, N.S. -- Provincial inspectors say a collapse at Canada's only operating underground coal mine saw about 60 square metres of roof fall into the entrance tunnel, significantly restricting access to the Cape Breton colliery.

There were no injuries in the fall, which occurred on the weekend and become public on Monday.

Scott Nauss, the province's senior director of inspection compliance, says after visiting the mine in recent days his staff has learned a slice of roof approximately 1.5 metres in depth came down.

He says that significantly blocked access to the Donkin coal mine's kilometre-long entry shaft.

The Nova Scotia Labour Department has issued an order that Kameron Collieries hire an expert to determine the cause of the latest rock falls in the mine as well as a plan to prevent a reoccurrence.

Nauss said unlike earlier rock falls closer to the rock face, last weekend's collapse is in an area supported by steel trusses, a system that had been in place since 1984.

The areas of the mine closer to the rock face is supported by roof bolts driven into the ceiling.

He says the company is responsible for hiring an expert to examine the area to understand why, after 35 years, this occurred in an area of the mine that is heavily used by workers.

"The inspection is ongoing and we will be monitoring the situation," said Nauss in an interview on Tuesday.

A spokesman for Kameron Coal has written in an email the roof that fell hasn't had problems since the shaft was created.

"The area and nature of this event is unrelated to the stress related issues experienced in the last half of 2018," he wrote.

Kameron Coal's operations in Cape Breton were suspended for just under a month in late December before the company was allowed to partially resume activities in one portion of the mine while it prepared a revised roof support plan.

The roof plan approved on May 7 allowed the company to mine in two sections of the Donkin mine totalling 730 metres of added rock face.

The last suspension of mining at Donkin due to a roof collapse occurred after Christmas, resulting in the province ordering the company to seek independent advice on a fresh roof plan.

It was the second collapse that month.

The December collapses came 11 weeks after a six-day closure in October, which was ordered after the company didn't report two massive cave-ins within the required 24 hours.

Inspection documents say both reported collapses had spanned the entire six-metre width of a passage, as slabs of rock fell and left a ceiling gap up to almost four metres deep. The first rock fall ran over 18 metres along the underground roadway, while the second was about a third of the length of a football field.

-- By Michael Tutton in Halifax