US police have been criticised by Occupy Seattle protesters for allegedly using disproportionate force when they pepper sprayed activists, including an old women and pregnant teen.

The incident occurred during a downtown rally in support of the Occupy Wall Street demonstrators, who were evicted from their camp in a park in Lower Manhattan earlier in the week.

Protest organisers say the police indiscriminately sprayed mace at peaceful protesters and released a written statement expressing support for an "84-year-old woman, a priest and a pregnant woman who as of this writing is still in the hospital".

A photo showing Dorli Rainey, an activist who has supported liberal causes in the Seattle area for decades, being cared for by fellow activists in the immediate aftermath of the police incident appeared on news websites around the world.

Jeff Kappel, the chief of Seattle police, told reporters that pepper spray "is not age specific. No more dangerous to someone who is 10 or someone who is 80."

Kappel added that police "probably wouldn't be using pepper spray" if it were harmful to the general public, although he didn't clarify in what circumstances the use of a harmful chemical on the public would be justified.

Kappel said plenty of verbal warnings were given to protesters attempting to block intersections and streets during rush hour and that pepper spray was used against "subjects who were either refusing a lawful order to disperse or engaging in assaultive behavior toward officers".

Six people were reportedly arrested in the clashes, which were the first of their king in Seattle in weeks.

Police authorities in New York were accused several weeks ago of indiscriminately pepper spraying peaceful protesters, with several videos posted online showing a group of stationary girls being targeted directly in the face by an officer.

The officer involved in that incident is facing an internal disciplinary hearing and could lose ten days vacation pay.

Seattle Mayor Mike McGinn released a statement saying he was sorry for those peaceful protesters who were maced.

"To those engaged in peaceful protest, I am sorry that you were pepper-sprayed," said McGinn, but Occupy activists are calling for investigations into the alleged violations of civil rights occurring in police raids around the country.

During the raid on the Occupy Wall Street movement's camp in New York City, protesters' private property was allegedly damaged or destroyed by New York police officials with riot-gear-clad police using force against those who tried to protest the destruction of private property.