One of Hong Kong's main highway links, the Cross-Harbour Tunnel, reopened early on Wednesday as a siege of the nearby Polytechnic University appeared to be drawing to a close with university officials declaring that no protesters were left on campus.

Hong Kong authorities hope that a lull in clashes over the weekend during local elections, where pro-democracy candidates secured an unprecedented landslide victory, will be maintained after nearly six months of turmoil.

Chinese authorities reiterated the need "to stop the violence and restore order" after the election.

More:

• Hong Kong's Carrie Lam offers no concessions despite poll rout

• Hong Kong protests: Are police using excessive force?

• Hong Kong democrats score historic victory amid continuing protests

Reuters also reported that China's leaders had set up a crisis command centre in the Chinese tech hub of Shenzhen, just across the border from Hong Kong, to deal with protests that have become the biggest populist challenge since President Xi Jinping came to power in 2012.

Despite the euphoria among protesters over the electoral victory, in which democracy advocates swept about 86 percent of the 452 district council seats, fresh protests are planned for the weekend, including a "no tear gas to children march".

The city-wide elections drew a record turnout and were seen as a vote of no-confidence against Beijing-backed Hong Kong leader Carrie Lam over her handling of the financial hub's worst crisis in decades.

Call for resignation

The opening of the Cross-Harbour Tunnel in the early hours of Wednesday came after anti-government protesters barricaded themselves inside the Polytechnic University and blocked the tunnel mouth almost two weeks ago.

Toll booths were smashed, fires lit and bricks thrown onto the highway, severely disrupting traffic between Hong Kong island and the Kowloon peninsula.

Hong Kong television showed a steady flow of vehicles surging into the tunnel after it reopened.

Police still guarded the perimeter of the Polytechnic University as a security team prepared to scour the campus for a second day, looking for protesters who may still be hiding in the maze of buildings.

The red-brick university was turned into a battleground in mid-November when nearly a thousand protesters barricaded themselves inside and clashed with riot police in a hail of petrol bombs, water cannon and tear gas.

Police later formed a security cordon around the campus to trap those inside, eventually making hundreds of arrests.

A small number are still believed to be inside.

But later on Wednesday, a university official said they had not found any protesters left on campus, signalling the end of the siege.

"We have tried our best to handle this matter. We have already done what we could do. We hope we can re-open the school soon to start our renovation work and reduce the impact on our students and our research projects," said Polytechnic University Executive Vice President Dr Miranda Lou.

One Hong Kong newspaper, Sing Pao, published a front-page spread for the second successive day calling for Lam's resignation.

"Hong Kong people have had enough, Carrie Lam quit," it read.

Demonstrators are angry at what they see as Chinese meddling in the freedoms promised to the former British colony when it returned to Chinese rule in 1997.

China denies interfering and says it is committed to the "one country, two systems" formula put in place at that time.