Hawke's Bay hosted two weekend rallies against the sale of legal highs.
Protesters gathered outside the Adult Selections store in Dickens St, Napier, on Saturday afternoon.
A Hastings rally began outside The Warehouse in Karamu Rd later in the afternoon.
The rallies were part of a nationwide campaign to ban the sale of synthetic cannabis.
Event organiser Chantelle Brown, whose son had been affected by the drug, said at least 350 people gathered outside Adult Selections in Napier.
"The number of customers still coming and going from the store shocked us," co-organiser Nicky Prisk said.
"A few people abused us."
Adult Selections was the only store selling synthetic cannabis in the region, after the indefinite suspension of two Hastings stores' licences.
Napier Mayor Bill Dalton, who advocated a blanket ban of all psychoactive substances, was in attendance.
"I was absolutely heartened by the support by people from Hawke's Bay and Gisborne," Mr Dalton said.
"At the end of the day, this drug is relatively new to society and we need to take the opportunity to stamp it out before it becomes entrenched."
Hastings district councillor Henare O'Keefe, Labour MP for Ikaroa-Rawhiti Meka Whaitiri and Labour Napier candidate Stuart Nash were also in attendance. Maori TV presenter Te Hamua Nikora came from Gisborne to MC the event.
"So many parents, families and communities destroyed by the drug came together to rally against it in 23 towns," Mrs Brown said.
"They say it [synthetic cannabis] can't be harmful if people aren't dying from it but we are the guinea pigs - we are the research."
A "Ban Synthetic Cannabis NZ Wide" Facebook page associated with the rallies had garnered more than 30,000 likes by yesterday.
Mrs Brown said the page had sparked "thousands of messages" from people asking for help with the drug.
Licence suspensions for two Hastings stores were extended indefinitely in late March as their appeals were processed by the psychoactive substances appeals committee.
Synthetic cannabis was still being sold from the Napier Adult Selections store.