Kuwaiti riot police on Sunday fought with tens of thousands of angry protesters, using tear gas, sound bombs and rubber bullets as activists reported several people injured and many arrests.

Witnesses said that they saw at least 10 men on the ground apparently after inhaling tear gas, and former MP Abdullah al-Barghash told AFP he saw injured men being taken to hospital in ambulances.

Barghash and other activists put the number of protesters at more than 100,000, which would be the largest gathering in the history of the Gulf state, but independent onlookers estimated the crowd at more than 30,000. Police made no estimate.

The opposition called the demonstration to protest against a decision by Emir Sheikh Sabah al-Ahmad al-Sabah to amend the electoral law. Activists claim the change is aimed at electing a rubber-stamp parliament.

Riot police earlier prevented protesters from gathering at three sites set by organisers, using tear gas and batons to disperse them and arresting several people including former Islamist MP Waleed al-Tabtabai.

Later organisers asked protesters to gather at an alternative site in the capital where demonstrators cut off the country's key seaside Arabian Gulf Road for several hours.

Masked police in full riot gear repeatedly fired tear gas and sound bombs and later used rubber bullets in a bid to disperse the crowds led by former opposition MPs.

"It looks like a battlefield," Mohammad Rashed, a private sector employee, told AFP as he left the scene, accompanied by his wife and other relatives.