Hong Kong: Presidents of nine Hong Kong elite universities have demanded Carrie Lam's government find an immediate political solution to restore safety and public order, while conceding multiple campuses "are now under protesters' control".

In a statement, the leaders said violence had rapidly escalated in Hong Kong this week and some staff and students had left campuses out of fear for their safety, as universities were challenged "in the most fundamental way".

A woman walks past Hong Kong riot police clearing up a road in the Central district of Hong Kong on Friday. Credit:AP

Police and government ministers had ramped up pressure on the leaders on Friday, accusing key universities of becoming "powder kegs" and "breeding grounds for criminals".

The comments added to speculation that riot police were preparing to storm campuses, as the Cross-Harbour Tunnel and a key highway remained blocked by protesters based at nearby universities.