Maritime New Zealand has announced that all beaches from Mt Maunganui to Maketu Point are closed as of midday on Thursday.
About 500 oil clean-up workers were at beaches again on Thursday and collected tonnes of polluted waste.
The agency says it is clearing the beaches so that the oil clean-up from the Rena spill can be carried out unhindered and police can monitor containers from the ship washing ashore. People who break the restriction will be told to leave, but will not be fined or arrested.
Maritime New Zealand says people who want to volunteer to help should phone 0800-645-774 or visit the website of the Bay of Plenty Regional Council.
Tauranga mayor Stuart Crosby says about 1500 people have registered so far and volunteers are being organised into teams so they can be trained to deal safely with the oil.
Earlier on Thursday, Papamoa beach was again covered with a thick oil slick brought in by the morning tide. A large crowd of people - many of whom had helped clear the beach of oil the previous day - gathered to watch. There is a strong smell of oily tar.
On nearby Mt Maunganui beach, two shipping containers have washed up. One is stuck firmly in the sand and has ruptured, spilling its contents onto the beach. Police are at the beach to keep onlookers away.
Maritime New Zealand says that while severe weather has hampered salvage efforts aboard the Rena, it has helped break up the oil that leaked.
Oil easier to clean up if it comes quickly
Experts assessing the amount of oil washing ashore say they may know in the next few days how long it will take to clean it up.
The chair of coastal science at Waikato University, Chris Battershill, says it is easier to clean up the oil if it arrives in significant amounts in a short time-frame.
Professor Battershill says experts are currently expecting the clean-up to be much quicker than the operation that followed a 270-tonne oil spill in Queensland, which took 18 months to clean up.
He says the initial use of dispersant on the oil may have done long-term damage to the marine environment.