Thirty-seven civilians were killed and more than 60 wounded when gunmen ambushed a convoy transporting workers of Canadian-based gold miner Semafo in eastern Burkina Faso, regional authorities said Wednesday.

The mining firm, which is headquartered in Montreal, earlier said the attack happened about 40 kilometres from the mine.

The convoy, escorted by military personnel, included five buses transporting Semafo employees, contractors and suppliers.

"Canada condemns today's attack against a convoy of workers of the Canadian mining company SEMAFO, which also targeted security forces protecting them," Angela Savard, a spokesperson for Global Affairs Canada, told CBC News. "To date, we have no reports of any Canadian citizens being affected.

"We offer sincere condolences to the families and loved ones of the victims, and wish those injured a speedy recovery."

The attack is the deadliest in recent years as the military struggles to contain Islamist violence that has overrun parts of Burkina Faso, located in West Africa. Semafo tightened security last year following armed incidents near two of its mines in the country.

The death toll, provided by the office of the governor for the Est region, does not include an unknown number of the security forces who may have been killed in the attack. The toll was likely to rise as there are a large number of people still unaccounted for, according to a security source.

Two security sources said the military vehicle leading the convoy was struck by an IED on a stretch of road where there is no cellphone network.

Shortly after the initial explosion, an unknown number of gunmen opened fire. One of the sources said it appeared that they targeted the buses as well as the military escort, which was unusual.

In December, a police vehicle was attacked on the same road, resulting in five deaths.

When contacted by Reuters, a Semafo spokesperson said: "At this point, we do not have full information and are not in a position to add to this morning's release."

Semafo said the Boungou Mine site remains secured, and its operations are not affected. Semafo operates the Mana and Boungou Mines in Burkina Faso.

On Wednesday afternoon, the company's stock price fell 11 per cent to $3.49 on the Toronto Stock Exchange.

Once a pocket of relative calm in the Sahel, Burkina has suffered a homegrown insurgency for the past three years, which has been amplified by a spillover of jihadist violence and criminality from its chaotic northern neighbour Mali.

After last year's incidents, which Semafo said were the work of "armed bandits," the company reinforced its escorts and decided to transport all expatriate employees by helicopter between the Boungou Mine and Burkina's capital Ouagadougou.