The unprecedented peacetime restrictions, which will last for at least three weeks, were brought in to prevent the state-run National Health Service (NHS) from being overwhelmed as the number of deaths in Britain rose to 335.
Aerial views of London showed some shopping centr car parks and Vauxhall railway station virtually deserted.
Not everyone though was abiding by the tough measures.
Social media images showed London Underground trains were still packed with commuters and large retail chain, Sports Direct, suggested it wanted to stay open.
The curbs on movement, under which people should only leave their homes for very limited reasons such as going to supermarkets or once a day for exercise, were announced in a national address by Johnson late on Monday.
He had resisted bringing in lockdowns which other European countries have introduced, but earlier advice for Britons to avoid gatherings was being widely ignored with people flocking to parks and beauty spots.