Belfast is braced for a potentially violent night.
Orangemen's so-called "Tour of the North" is getting underway with a parade planned through the flashpoint Ardoyne area.
The Order is staging the march approved by the Parades Commission, but which Catholic residents are opposed to.
Sinn Féin leader Gerry Adams has appealed for calm.
"There is the possibility of an Orange parade into my constituency this evening," he said.
"There is an unwanted parade into Ardoyne this evening, we have appealed to the marching orders to accept that we all put up with thousands of Orange parades and these contentious ones should not be forced into nationalist areas," he said.