Canadian truckers were blocking the busiest crossing with the United States, as Prime Minister Justin Trudeau prepared to face legislators later in the day to discuss the growing crisis.
Drivers demanding an end to federal Covid-19 vaccine mandates for cross-border traffic first arrived in Ottawa on 28 January and gradually took over the centre of the Canadian capital.
As police slowly started to take back control the protesters - many of whom are demanding that Mr Trudeau quit - moved their focus to the Ambassador Bridge linking Detroit and Windsor.
Trucks started blocking traffic late last night and a Canadian government website showed that the bridge was shut in both directions at one point.