AMSTERDAM—Thousands of protesters packed Amsterdam’s streets on Sunday in opposition to the government-imposed COVID-19 restrictions. Authorities were granted stop and search powers at several locations across the city and scores of riot police vans patrolled neighborhoods where the demonstrators marched with banners and yellow umbrellas. Regular anti-lockdown protests are held across the country and Sunday’s large gathering was joined by farmers who drove to the capital and parked tractors along the central Museum Square. The crowd played music, chanted slogans, and then marched along thoroughfares, blocking traffic. The Netherlands had one of Europe’s toughest lockdowns for a month through the end-of-year holidays. Amid growing public opposition, Prime Minister Mark Rutte on Friday announced the reopening of stores, hairdressers, and gyms, partially lifting a lockdown. Rutte’s government ordered the lockdown in mid-December. Non-essential stores, hairdressers, beauty salons, and other service providers were allowed to reopen on Saturday under strict conditions. Bars, …