The mine had two chambers – and they were a place of safety and contained essential supplies such as water and food.
“The rescue teams have opened the refuge chamber (estimated to be at a depth of about 570m), unfortunately it is empty,” Reuters quoted the government’s information service as saying.
The mine, which is owned by Canadian firm, Trevali, has a depth of more than 710m (2,329ft) – and a second rescue chamber was located at the bottom.
A search was ongoing, according to the same information service, and will continue until any person was found alive or dead.
The mine was located about 100km (60 miles) west of the capital, Ouagadougou.
Last week, the Canadian mine owners said search crews were working 24 hours a day to find the workers.
The case had caused outrage in Burkina Faso, as rescue operations only got underway following protests and a sit-in at a government building at a nearby town five days after the floods.
The area saw heavy thunderstorms on April 16 that cut off electricity and communications.
The families of two of eight miners trapped by flood waters in a zinc mine in Burkina Faso last month were hopeful the workers would be found alive.
“It’s been three weeks of sleepless nights for all of us,” a cousin of one of the trapped men told the BBC.
There has been no contact with them and a wife of another of the men said she was unhappy with the rescue efforts.
It was not known if those working more than 520m (1,706ft) below ground reached two available refuge chambers.
The Canadian owners of the mine – which is about 100km (60 miles) west of the capital, Ouagadougou – said search crews continued to work 24 hours a day.
Specialised equipment had been brought in from Ghana and South Africa to speed up the rescue efforts at the mine that has a depth of 710m.
Trevali Mining says 32 million litres of water have so far been pumped out of the mine, allowing rescue workers to reach 550m below ground. –Reuters/BBC