A worker cutting a pipe has caused an explosion in Christchurch's Yaldhurst this morning. 

Emergency services were called to the incident at a rural property on Pound Rd at 11.30am. 

A Fire and Emergency NZ spokesman said a pipe being cut caused the explosion. 

St John was called at 11.22am today to an incident on Pound Rd in Yaldhurst, Canterbury. 

Two ambulances, a rapid response unit and a manager responded to the scene. St John treated and transported one patient in a critical condition to Christchurch Hospital. 

- by Devon Bolger, NZ Herald