"The area where the fire was started is well used by members of the public so someone must have seen something and we urge them to come forward."
A large scale sprinkler line would meanwhile be installed from George Conway Dr down to the south of the subdivision along the back fences.
A heavy duty grader would also be used to scrape off the dry grass to create a bare earth break and minimise the risk of hotspots spreading.
Sprinklers would run for the next few days to keep the area dampened down.
Access in the area is restricted to residents only.
The Taylor River walkway near West Mount school is closed and members of the public have been directed to stay well away from the area.
A total fire ban remains in place across Marlborough.