The oil washing up on Manawatu beaches is unlikely to spread further north into the Rangitikei coastline.
A clean-up led by Horizons Regional Council has been under way since Monday afternoon after the discovery of oil washing up on a 10km stretch of coastline from Foxton Beach to 500m north of Himitangi.
It is still not known where the oil came from.
Council on-scene commander Ian Lowe said the response team had checked as far as Tangimoana but no new oil had hit the coast.
"Samples will be sent to a laboratory to help determine their source, which is still unknown. However, the focus is very much on the clean-up at this stage," he said.
Maritime New Zealand has also been notified of the spill and is looking at trajectory models and vessel logs to try and determine a possible source.
"Any risk to marine life is considered minimal," Mr Lowe said.
Meanwhile, people are being asked to stay away from the beach.
Yesterday, council staff were joined by the Department of Conservation, volunteers, Ngati Kauwhata and Rangitaane o Manawatu members to help clean up oil from the shoreline.
The crew of about 20 people are working to remove oil from the beach using shovels, gloves and bin liners and, at this stage, the clean-up is anticipated to take at least a couple of days.
"We are continuing to check to ensure oil hasn't extended any further but, at this stage, it appears to be located between Foxton Beach and 500m north of Himatangi Stream only."
The results of the oil testing are expected by next week.