The Shell to Sea protest group's Day of Action in Co Mayo has sparked off violent scenes and one protestor was reportedly taken to hospital with neck and back injuries.
Members of the Shell to Sea group also say a number of other protestors sustained head injuries at Bellenaboy but did not need hospital treatment.
About two hundred people were staging a sit-down protest in an effort to prevent Shell workers entering the construction site of the new gas terminal.
But Gardai succeeded in moving the convoy of workers through to the site.
Demonstrators have been staging protests there every morning since October 2.
Meanwhile, demonstrations will take place at Shell Headquarters around the world today to mark the 11th anniversary of the execution of Ken Saro-Wiwa and eight other anti-Shell activists in Nigeria.
A wreath will be laid at Shell's Headquarters in Dublin this lunchtime.