Dozens of people were still missing Thursday after an ambush on workers near a Canadian-owned mine in Burkina Faso killed at least 37 and wounded 60 in the worst such attack in the West African nation in years.

Quebec-based gold miner Semafo said five of its buses with a military escort came under fire on the road leading to its Boungou mine in the eastern region of Est, about 40 kilometres from Boungou, on Wednesday.

The assailants' identity was unclear, but Burkina Faso is struggling to combat surging Islamist violence in the remote eastern and northern scrubland areas.

Burkina Faso's president vowed Thursday that security forces will bring the "terrorists and their accomplices" to justice.

"Once more our people are in mourning because of terrorist groups that are multiplying, murderous actions against our civilians and our defence and security forces," President Roch Marc Kaboré said in a televised address.

Semafo said the Boungou mine site remained secured, although it has suspended operations as a result of the attack.

It was unclear how many people were in the convoy, what their nationalities were or how many were missing. Two security sources told Reuters that potentially dozens were still unaccounted for.

There were no reports of any of any Canadians being affected, according to a spokesperson for Global Affairs Canada.

One miner was shot in the leg but survived because the bodies of other victims fell on top of him, shielding him from the hail of bullets, his brother said.

"There were more and more shots and then because the others were on top and he was underneath, God protected him," Benjamin Compaore said, speaking outside the Ouagadougou hospital where the wounded were being treated and distraught family members gathered.

Some questioned why the authorities had not yet provided a full casualty list.

Theodore Silga said his younger brother Gilbert, 26, had been on one of the ambushed buses. "The people working with my brother said they have not heard from him."

Semafo tightened security last year following attacks that killed three workers and five security officials. The measures included flying expatriate employees to mines in helicopters and providing ground military escorts for Burkinabe employees.

Two separate sources, who have worked at the mine, said the convoy left weekly carrying about 250 local staff, usually in five buses of 50 to 60 people each.

Listen to an expert on The Current last January discuss the growing armed presence in Burkina Faso

Canadian citizen Kirk Woodman was abducted and killed in Burkina Faso this week, while Quebec woman Edith Blais went missing in the country weeks ago. We speak to two experts about who is behind the violence, and why. 19:06

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

Wednesday's attack was the worst since groups with links to ISIS and al-Qaeda began targeting the landlocked nation with high profile attacks in January 2016.

Then, armed al-Qaeda militants killed 32 people in a raid on a popular cafe and hotel in Burkina Faso's capital Ouagadougou.