Hundreds of flights in and out of Hong Kong have been canceled Monday as pro-democracy demonstrators carried out strikes and protests on the biggest day of demonstrations so far this summer. Hong Kong’s leader warned Monday of a “crisis” engulfing the city as activists shut down subway and rail lines and airlines pulled more than 200 scheduled flights. Service was suspended on the main subway line on Hong Kong Island, disrupting the morning commute for hundreds of thousands of workers. Activists have also built road blocks out of traffic cones and street barriers, symbolically locked together by umbrellas, on main routes into the city. Hong Kong Chief Executive Carrie Lam said the disruptions “have seriously undermined Hong Kong’s law and order and are pushing our city, the city we all love and many of us helped to build, to the verge of a very dangerous situation.”