Liverpool has "absolutely nothing to lose" by taking part in the first trial of whole city coronavirus testing in England, the city's mayor has said.
Everyone living or working in Liverpool will be offered repeat tests, whether or not they have symptoms.
Mayor Joe Anderson said the testing pilot could save lives, stop hospitals being overwhelmed and "get the city out of tier three restrictions".
The pilot will last for approximately two weeks, the government said.
But Liverpool's director of public health Matthew Ashton told BBC Breakfast it could last longer, saying he wants "to make sure [the pilot is] long enough for us to be able to see the impact".
People will be offered a mix of existing swab tests and new lateral flow tests, which could provide a result in 20 minutes without the need to use a lab.
New test sites have been set up across the city, in schools, universities, work places and care homes.
Six test centres for people who do not have symptoms will be open from 12:00 GMT until 19:00, with more sites planned.
There are appointments available at different testing centres for those with symptoms.
About 2,000 military personnel are helping deliver the tests.
Mr Ashton said testing was open to "absolutely everybody" - whether symptomatic or asymptomatic - and stressed that further testing sites would open in the coming days.
He said the region would have up to 35 mobile testing sites, which can each do 400 tests a day, and 50 alternative testing sites, which can each do 1,000 tests a day.
Asked whether the pilot would last long enough to produce any "tangible" results, Mr Ashton said: "We are working at pace to develop this, including with our national colleagues, and one of the things I want to make sure is that the pilot lasts long enough for us to be able to see the impact of it.
"We are open for an initial 10 days, but I'm not getting the readings that it's 10 days and turn off. We are able to expand it, extend it, to make sure the pilot fits."
He added: "There may be elements that don't go beyond the 10 days, and we're talking about that right now, but the point of this is to get the city tested.
"In order to do that we have to have capacity in for a long enough period to get people tested."
On the aim of the pilot, Mr Ashton said: "Success is lowering the levels of the virus in the city and exiting out of the national lockdown in a much stronger position."
Lt Gen Tyrone Urch, who is leading the deployment of the army to help with testing, told BBC Radio 4's Today programme troops had been arriving in Liverpool "over the last day or so".
He said they could help with planning, administering the tests, and offering logistical support - such as in distribution, clerical roles and as drivers.
'Highest viral loads'
The new lateral flow tests will detect people with the "highest viral loads" - assumed to be the most infectious people, according to Dr Emily Adams, a senior lecturer at Liverpool School of Tropical Medicine.
The scientist told BBC News that as this would detect about "three-in-four or four-in-five" cases, it was important people still follow guidelines to self-isolate if they show symptoms and get a regular swab test.
But she said the lateral flow tests "work very well in an asymptomatic population", and that she was "optimistic" they would have a big impact in Liverpool.
Meanwhile, a leading scientist has warned the NHS Test and Trace system has made no difference to the spread of coronavirus in the UK.
James Naismith, professor of structural biology at Oxford University, told BBC Radio 4's Today programme the system "hasn't been effective at all" and was only reaching a fraction of the number of people who should be contacted.
He said: "The point of the system is you need to get a large number of the contacts and break the chains of transmission at a large scale for the Track and Trace system to be effective.
"Given that you miss over half right at the start and then as you walk through the various losses through the system you are actually reaching 20% of the contacts you want to reach overall.
Given where we are now in infections, it is not until we get proper mass testing that the system can really recover."
Liverpool City Region was the first area to be put into the very high alert level of England's three-tier system of Covid-19 restrictions, on 14 October. Since then, cases have fallen.
A national lockdown in England began on Thursday.
The latest figures showed Liverpool recorded 318 cases per 100,000 in the week up to 2 November. Across England overall, the rate was 236 per 100,000.
Mr Anderson said Liverpool was involved in tuberculosis screening in 1959 and had always been "pioneers in public health".
Prime Minister Boris Johnson said he was "hugely grateful" to the people of Liverpool for taking part in the pilot.
He said he hoped that "together we can get that great city on top of the virus".
A spokesperson for the Department of Health said the pilot "was planned to last for approximately two weeks".