About 100 protesters and 11 police officers have been injured as Kuwaiti police used tear gas and rubber bullets during clashes with demonstrators.
Tens of thousands of people had gathered across the capital, Kuwait City, to march on the Seif Palace, which houses offices for the emir, crown prince and prime minister, as part of a protest against changes to the electoral law, which the opposition described as a "coup against the constitution".
But several groups taking part in the so-called Dignity March were quickly surrounded by riot police who used tear gas and stun grenades in an attempt to disperse them, witnesses said.
The director of the Kuwait Society for Human Rights, Mohammad al-Humaidi, said on Twitter: "The number of wounded protesters in hospital has exceeded 100 after riot police attacked them."
Former opposition MP Abdullah al-Barghash said he saw a number of injured men being taken to hospital in ambulances.
"The way demonstrators were dealt with is unprecedented in Kuwait," Mr Barghash said as he led several hundred protesters, some wearing orange straps to signify the call for change.
Most of the injured suffered from tear gas inhalation or from baton bruises, a medical source told Reuters.
As the clashes took place, the emir received members of the ruling Al Sabah family, which has been in power for over 250 years, who reiterated their loyalty to him, official news agency KUNA reported.
The opposition decided to take to the streets after the government announced last week it was calling elections for December 1 and would alter the electoral law "to preserve national unity".
The changes will allow voters to choose only one candidate per electoral district, making it difficult for the opposition to build political alliances.
"The decree is void, void," some protesters chanted during the protest.
The emir, Sheikh Sabah al-Ahmad al-Sabah, who is referred to as "immune and inviolable" in the constitution, dissolved parliament on October 7.
It was the sixth time the oil-rich state and key US ally had disbanded its legislature since early 2006.
However, the Gulf nation's oil wealth and generous welfare state have so far helped Kuwait avoid the kind of "Arab Spring" protests that toppled leaders elsewhere in the region.