Experts are examining several ground holes that have appeared in Quebec City's Charlesbourg's district. (Radio-Canada)Engineers and geologists are examining dozens of deep holes that appeared in the ground in Quebec City's north end this week, as residents are being urged to leave their homes for safer locations.

City officials served evacuation papers Wednesday to about 15 homes and one business in Quebec City's Charlesbourg district, where nearly 40 holes have been reported.

The holes, ranging between five and eight metres wide, have appeared this week in various fields, and on one residential driveway.

The deepest hole is about five metres deep.

Some of the holes have closed, but the remaining gaps are mystifying officials.

"The field is is like, there is nothing, no trees or anything and you see everywhere some holes, some deeper than others, like 30 or 40 holes everywhere on the field. You can see this is not normal. You can see this is a problem on this land," said city spokesperson François Moisan.

Some of the affected fields used to be sandpits, but experts are running tests with surface radar instruments to analyze the soil.

Evacuation is optional, but strongly recommended, Moisan said.

"The city is very prudent and we ask people to leave their house because there is some danger. We don't know what kind of danger, we don't know if it's a real threat to their property but we prefer to take no chances and ask them to leave."

A map of the affected area in Quebec City's Charlesbourg neighbourhood. (CBC/Radio-Canada)Moisan estimates at least 40 residents have heeded the optional evacuation recommendation.

Given that there is rain in the forecast, I prefer to spend the weekend in a hotel," Charlesbourg resident Jonathan Roussel told Radio-Canada.

Other residents who chose to leave their homes are using Red Cross emergency services.

Others, like Pierre Bourdeau, are willing to take the risk and stay put.

"I inspected my house, and there are no fissures, nothing," he told Radio-Canada. "I've never even had water in my basement. Why would I leave?"