Train stations across the south of England have been deserted as rail workers take to picket lines.
Members of the National Union of Rail, Maritime and Transport Workers (RMT) are striking over job cuts, pay and working conditions.
Limited rail services have been running in Hampshire, Dorset, Oxfordshire and Berkshire as a result.
Bournemouth Train Station has been heavily impacted, with no trains running at all.
RMT General Secretary Mick Lynch said staff were being asked to accept thousands of job cuts, reduced pensions, worse terms and conditions and a cut in real-terms pay as living costs soar.
The prime minister has said the country must "stay the course" during the rail strikes, as he urged rail bosses and unions to agree on a deal.
Commuters were nowhere to be seen at Dorset's usually busy Bournemouth station - with only three taxis optimistically waiting for customers.
One driver, Abdelkader Hamdi, said: "I hypothetically agree with the strikes, the cost of living crisis is affecting everyone at the moment.
"It cost me £2 per litre for diesel this morning. I understand.
"It will though have an impact on my income and I hope it all gets better for the summer season."
Strikes are also expected on Thursday and Saturday, when no trains will run again from Bournemouth, and there will be limited services on the days in between.
RMT workers gathered outside Bournemouth station and also Basingstoke, in Hampshire, to strike.
Passengers in Southampton and Winchester said they "sympathise" with those striking, but added it meant their days were going to be "much longer" because of revised timetables.
Ted, a commuter waiting on the platform at Winchester Train Station, said: "Everyone would like a pay rise, everyone has potentially got the threats of job cuts and redundancies after the pandemic, but we are trying to restart the economy a bit and this week is going to be a real dent to the economy unfortunately."
Eliza, an occupational therapist for the NHS who was travelling from Southampton Central, said she sympathised with those striking as a fellow public service worker.
"I know that they are probably overworked and underpaid just like us but it's a bit frustrating and just makes getting to work much more difficult and makes my day much longer," she said.
BBC South reporter Matt Treacy said trains from Reading into London were empty at the height of rush hour.
There are usually 30 morning services to Paddington but due to strikes only four were running.
Merryn, an east London teacher who was travelling from Twyford in Berkshire via Reading Train Station, said: "There's no choice about me getting to work.
"It's far quieter than usual, so I think most people have taken the warning seriously which is very convenient for those that can't."
Another commuter travelling through Oxford Train Station said their journey to work was "way harder than usual".
Passenger Ryan Hairsine said: "It's obviously having an effect on the country, it's normally jam-packed here and they [the RMT strikers] know what they're doing and they've stuck by it.
"I'm happy to take the hit if it makes it better."