Police in the US city of Portland have made arrests and seized fireworks, hammers and a rifle during demonstrations on the night after voting in the US presidential election.

Oregon Governor Kate Brown activated the state's National Guard in response to "widespread violence".

Portland Police said 11 people were arrested in the city's downtown area while the New York Police Department (NYPD) said it made about 50 arrests in protests that spread across the city.

"All of the gatherings that were declared riots were downtown. We have made ten arrests", a Portland Police spokesman said in a statement.

Demonstrations were also seen in a few other US cities last night as activists demanding that vote counts proceed unimpeded rallied in several cities, including Atlanta, Detroit and Oakland.

Earlier, about 100 people gathered for an inter faith event before a planned march through downtown Detroit, in the battleground state of Michigan, to demand a full vote count and what they called a peaceful transition of power.

Local partners of Protect the Results - a coalition of more than 165 grassroots organisations, advocacy groups and trade unions - have organised over 100 events planned across the country between yesterday and Saturday.

Demonstrators marching on Fifth Avenue in New York

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Heading into the election, the United States had seen months of protests following the death in May of George Floyd, an African-American who died after a Minneapolis police officer knelt on his neck for nearly nine minutes.

The demonstrations once again picked up momentum following the police shooting of an African-American named Jacob Blake in Kenosha, Wisconsin and the death Walter Wallace Jr who was killed by two officers in Philadelphia.

Portland has seen several demonstrations since Mr Floyd's death, particularly in the city's downtown area, with protests occasionally turning into clashes between demonstrators and police as well as between right- and left-wing groups.

The anti-racism protests have demanded an end to police brutality and racial inequality while the more recent demonstrations surrounding the election have demanded a full count of the votes cast on Tuesday.