Chief Executive of the Hong Kong Special Administrative Region (HKSAR) Carrie Lam Tuesday called on rioters who are still in Hong Kong Polytechnic University (PolyU) to leave peacefully and safely.

"It is our hope the issue could be resolved in a peaceful way," she said at a media session.

Tuesday marks the 10th day after the rioters gathering around PolyU took the campus as a stronghold. A staff member with the university, who declined to be named, told Xinhua that PolyU sent six work teams into the school buildings on Tuesday and they failed to find any rioter before noon.

While police announced on Monday that around 1,100 people had left the campus in a peaceful and orderly manner, the staff in PolyU said that about 30 rioters were believed to remain on campus, who could pose potential threat to people going into the buildings.

He admitted that lethal chemicals were missing from laboratories, some of which flammable and dangerous.

Rioters previously launched assaults on police officers, using lethal weapons including petrol bombs, bows and arrows, metal balls and bricks.

The nearby Cross-Harbor Tunnel, a major artery linking the Hong Kong Island and Kowloon, has been forced to close for more than two weeks with toll gates set ablaze and debris scattered on vehicle lanes.

On the ground of an open space inside PolyU, Xinhua reporters could see lots of unused petrol bombs, cans of cassette gas as well as bottles of cooking oil placed together with flammable liquid.

Handmade weapons were left everywhere. Plastic pipes were poked with four or five nails on each section, and were placed on the ground, which were believed to obstruct police.

The rioters also made slingshots and catapults, and used arrows to attack police. A Hong Kong police officer was struck in the calf on Nov. 17.

Police have repeatedly called on all people remaining inside PolyU to leave the campus peacefully as soon as possible.

They also planned to send a safety team into the university to negotiate with and offer medical assistance to the rioters remaining on campus.

"We would like to enter the campus at a proper time, so as not to agitate them," said Carrie Lam. "If the PolyU work teams do not success, or if they need our assistance, our safe team will be of help."