LISBON, July 8 (Reuters) - Scrambling to bring under control a worrying COVID-19 surge, tourism-dependent Portugal imposed stricter rules on Thursday, requiring holidaymakers to show a negative test, a vaccination certificate or proof of recovery to stay in hotels. Portugal"s new daily case numbers have been rising steadily in recent weeks, returning to levels last seen in February when the country was under a strict lockdown to tackle what then was the world"s worst coronavirus surge. Nearly 90% of cases are of the more infectious Delta variant and, as it quickly spreads, the country is left in a tight spot, finding it tough to salvage the usually busy summer season. Negative tests, vaccination certificates or proof of recovery will also be required to eat indoors at restaurants in 60 high-risk municipalities, including Lisbon and the city of Porto, on Friday evenings and at the weekend. "For a long time, the only measure we had to our disposal was limiting economic activity," said Cabinet Minister Mariana Vieira da Silva. "With the (EU) digital certificate, and the more frequent availability of tests, we have other ways of guaranteeing security." Holidaymakers and restaurant customers must use the EU digital COVID-19 certificate. Rapid antigen and PCR tests will also be valid, the minister said. Fast tests can be provided by hotels at check-in. The new rules, which also apply to other holiday accommodation like Airbnbs, come into force on Saturday. Children under 12 accompanied by a parent or guardian are exempt. Portugal"s restaurant association said "there were already too many rules and restrictions" which risk driving customers away. "This could destroy the ray of hope for many business people," it said. Customers and businesses who break the rules risk being fined, up to 500 and 10,000 euros respectively. The measure will allow restaurants to reopen for dinner on Saturday and Sunday in high-risk areas, where they were forced to shut earlier for the two previous weekends. A night-time curfew, already in place 45 municipalities, will be extended to a further 15 municipalities, including Faro, the main city in the popular southern Algarve. Portuguese police say they are struggling to keep young holidaymakers off Algarve"s streets at night. Portugal, population 10 million, reported more than 3,000 daily coronavirus cases on Thursday, bringing the total since the start of the pandemic to 899,295. Cases started to gradually increase after Portugal opened to visitors from the EU and Britain in mid-May. But daily deaths remain well below February levels with new cases primarily reported among younger, unvaccinated people. To tackle the increase, Portugal, which has fully vaccinated 40% of its population, has accelerated its vaccination rollout and managed to inoculate 600,000 people this week alone. The speedy campaign triggered long queues outside vaccination centres.