Some of America's iconic national parks are in danger of being overwhelmed by rubbish and could suffer significant damage due to the partial shutdown of the US government, conservationists have warned.

Donald Trump said he had "no choice" but to continue the shutdown, blaming Democrats as litter and human waste piled up at tourist areas around the country.

Dakota Snider, 24, who works in Yosemite Valley, said: "It's so heartbreaking. There is more trash and human waste and disregard for the rules than I've seen. It's a free-for-all."

The US government has been partially shut down for 11 days due to a standoff between Mr Trump and Democrats in Congress, who are refusing to authorise $5.7 billion to fund a large part of the president's proposed wall on the Mexico border.

Hundreds of thousands of public employees have been sent home, including rangers and other park staff.