Christchurch protestors have locked themselves to train tracks at Woolston.

30 Extinction Rebellion activists are sitting on tracks on the corner of Garlands and Opawa roads, attempting to block a West Coast coal train travelling to Lyttelton Port.

Spokesperson Siana Fitzjohn says about 50 others are standing alongside, chanting and drumming.

“In the middle of a climate emergency, we can't be digging coal up, using it locally or exporting it overseas.”

Fitzjohn says they've warned KiwiRail of the action.

Kiwirail Chief operating officer Todd Moyle says they respect people's right to protest, but safety has to come first.

He says people are free to protest outside the rail corridor, but trains are big, fast and can't stop quickly.

Moyle says by 11.30am, four freight trains had already been affected.