The vociferous crowd in Dunedin marched along George St carrying placards and chanting slogans such as: "TPPA, no way!" and "TPPA, taking people's power away".
Like other critics of the trade agreement - planned for 12 countries including the United States, Japan, Singapore, Australia and NZ - the protesters slammed the deal as an attack on democracy and a ''corporate power grab''.
They were also concerned the deal had been shrouded in secrecy.
Organiser of the Dunedin event, Jen Olsen, said concern was growing about the impact the TPPA could have on many aspects of New Zealand life.
"The TPPA gives greater powers to multi-national corporations to dictate to governments and to sue in off-shore tribunals if decisions go against them," she said.
The Dunedin march came as protesters planned to gather in up to 23 centres, including all New Zealand's largest cities. Demonstrations in Auckland, Wellington and Hamilton were scheduled to start at 1pm.
A speaker at the demonstration in Wellington initially said a "weather bomb" descending on the city meant a planned march on Parliament from Midland Park would not go ahead.
But a few hundred excited protesters chanted in favour of marching, so the group started making its way to the Beehive shortly before 1.30pm.
"TPPA, no deal, don't let corporations plunder and steal," went one chant.
Christchurch event organiser Gen de Spa said the protests would be peaceful.
"There will be chanting and that kind of thing because we've got a message to get out there. But it'll be fun, it'll be a nice day out.''
The Green Party said Kiwis were being sold a ''dud'' and there was too much secrecy around the TPPA.
''Information about the agreement has been made public only through leaks, despite repeated calls by New Zealanders to make the details public,'' Green Party trade spokesman James Shaw said.
''If the Government is so confident this deal is beneficial to New Zealand they should release the full cost-benefit analysis,'' he said.
''We aren't being told what benefits this deal will bring us...We know through leaks that the TPPA is a Bill of Rights for multi- national corporations.''
The deal put the interests of major corporations ahead of New Zealanders' health, environmental and democratic rights, Mr Shaw said.
''Make no mistake, this is a corporate power grab on a scale never before seen in human history,'' said Todd Rippon, Actors Equity New Zealand vice-president.
''This treaty is so repugnant that if a full text of the negotiations were released to the public tomorrow it would cease to exist by the end of the week because anyone with a brain and a gag reflex would reject it outright.''
Supporters of the TPPA, including New Zealand's Ministry of Foreign Affairs, said the deal would deepen economic ties and open up trade, boost investment flows, and promote closer economic and regulatory co-operation.
- additional reporting NZME
