Authorities have vowed to toughen a crackdown on illegal investment schemes after thousands of protesters took to the streets in central China at the weekend, state media reported Tuesday.

Demonstrators in Anyang, a city in Henan province, swarmed a train station on Sunday claiming they had been defrauded and threatening to take their gripes to Beijing, various reports said, in the latest protest to hit the country.

Photos posted online purportedly of the protest showed thousands of people and dozens of police, some wearing riot gear, on a street.

Police detained 21 protesters, the China Business News said. They also stopped demonstrators from boarding trains bound for the capital, according to a post on a weibo, a Chinese version of Twitter.

AFP calls to the Anyang city government went unanswered.

Anyang has been plagued by illegal investment schemes, which offer higher interest rates than banks. Many investors have been left out of pocket after the operators of the scams went broke and fled, previous reports said.

Authorities launched a crackdown in September, arresting more than 100 people and investigating more than 40 companies suspected of being involved in the multi-million-dollar schemes.

But the city government on Sunday admitted to "weak links in our handling of illegal fundraising schemes" and pledged to recover investors' money, the Anyang Daily said in a story carried on the city government's website.

Limited investment options and low interest rates offered by the major banks have prompted many Chinese seeking better returns for their money to invest in the country's property market and illegal get-rich-quick schemes.

The Anyang protest is the latest incident in China where residents have taken to the streets to oppose land seizures, pollution and perceived official corruption.

Last month residents of a village in the southern province of Guangdong faced off with authorities for more than a week after driving out local party officials they say had been stealing their land for years.

The revolt against officialdom in Wukan ended after a senior provincial official said their complaints about land seizures were reasonable and agreed to release detained villagers.

Locals of Haimen town, also in Guangdong, clashed with police last month after they blocked a highway to protest a planned power plant expansion, which authorities later promised to suspend.