The tentacles of Quebec's ever-expanding corruption scandal have reached into the home and headquarters of a mayor long considered untouchable.

About 70 investigators from the province's anti-corruption squad descended on Laval City Hall and the home of Mayor Gilles Vaillancourt Thursday, seizing documents and databases related to contracts handed out by Quebec's fastest-growing big city.

The raids come as corruption in government construction contracting is getting a thorough airing at the Charbonneau inquiry. Construction magnate Lino Zambito held the province in rapt attention this week as he accused mobsters, Montreal city employees and the political party of Mayor Gérald Tremblay of organizing an intricate system of kickbacks and illegal payments.

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Laval, a suburb just north of Montreal, has grown from a sleepy island of farmland and bedroom communities to an industrial and real-estate development hub with the population of Halifax in the 23 years Mr. Vaillancourt has ruled.

The city has long been reputed to be rife with shady dealings between officials, construction companies and developers, but despite damning media investigations and serious allegations by provincial politicians and local rivals, no police force showed interest in Mr. Vaillancourt – until now.

The investigators arrived at City Hall at about 4 p.m. and ordered all employees to leave immediately, a city spokeswoman said. Staff was told to take only their personal effects with them. Officers also searched the million-dollar home of Mr. Vaillancourt, a man nicknamed the "King of Laval" who has barely been contested since first becoming mayor in 1989.

Police also raided the offices housing the city's computer servers and engineering department as the Quebec corruption scandal spread, fueled by revelations at an inquiry hearing shocking allegations of kickbacks, illegal political financing and bribery.

"Police inspectors are still inside City Hall and they told us they would be there for a good part of the evening and even into the night," Nadine Lussier, a spokeswoman for the city of Laval, said from outside City Hall on Thursday evening. "We are fully co-operating with the authorities."

A spokeswoman for Quebec's anti-corruption squad would not comment on what the investigators are trying to find. "There is an investigation under way and the seizures are to find information to assist the investigation," said the spokeswoman, Anne-Frederick Laurence.

But opposition politicians in Laval said police were looking for evidence involved in the awarding of contracts in Laval. In fact, news of the raids was greeted with joy by Laval's opposition leaders who have difficulty getting elected or heard in Laval, where Mr. Vaillancourt has long had a stranglehold on city council.

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The opposition in Laval traditionally watches council proceedings from the public gallery. Mr. Vaillancourt's critics have asked for police investigations for years.

Opposition politicians say they have been raising concerns about the awarding of contracts in Laval for years. "We're not surprised by this," said David De Cotis, head of the Mouvement Lavallois party. "We see the same firms over and over getting contracts, and they contribute to the mayor's party. The system is broken in Laval."

The mayor wasn't home at the time of the raids and left City Hall in the morning. A spokeswoman said the mayor wasn't hiding and is prepared to go before the Charbonneau commission probing corruption in public contracts if asked to do so.

"He is very surprised" by the police raid, Johanne Bournival said.

At the Charbonneau inquiry, Mr. Zambito's public testimony has mostly concentrated on Montreal, but he has hinted the stink of corruption is as bad or worse outside the city.

He said Laval and other areas outside Montreal also have a closed system of rigged bidding on public works contracts, but, instead of mobsters, politicians run the system.

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When someone from outside would underbid on a contract, "they would just cancel the contract," Mr. Zambito testified. "In Laval, the Mafia wasn't present. There were other mechanisms to control things. … It was another game."

Media reports in Quebec have raised questions about the conduct of Mr. Vaillancourt. A La Presse investigation found a quarter of Laval public works contracts between 2001 and 2008 went to firms controlled by Tony Accurso, the construction magnate facing charges of corruption for dealings with other municipal governments.

A Radio-Canada report accused Mr. Vaillancourt of offering a $10,000 cash contribution to former provincial Justice Minister Serge Ménard when he was running for a seat in the provincial legislature under the Parti Québécois banner in 1993.

Mr. Vaillancourt has always denied any wrongdoing.