There has also been a renewed increase in protest activity as hostile sentiment against mainland Chinese strengthened over fears of viral transmission from mainland China, with many calling for the border ports to be closed and for all mainland Chinese travellers to be refused entry. Incidents have included a number of petrol bombs being thrown at police stations,[174] a homemade bomb exploding in a toilet,[175] and foreign objects being thrown onto transit rail tracks between Hong Kong and the mainland Chinese border.[176] Political issues raised have included concerns that mainland Chinese may prefer to travel to Hong Kong to seek free medical help (which has since been addressed by the Hong Kong government).[177][178]