People are advised to only travel by train if necessary, with just a fifth of services running.
Rail passengers across Britain are braced for a third day of strike action on Saturday, with disruption expected over the weekend.
Despite continuing talks, no resolution has been reached in the dispute over job losses, pay and conditions.
People are being advised to only travel by train if necessary, with just one in five services running on Saturday.
Some 40,000 members of the Rail, Maritime and Transport union walked out on Tuesday and Thursday this week.
Some commuters were able to work from home on the first two strike days, but there are several big events in London over the weekend, including a sell-out Rolling Stones concert in Hyde Park and Ed Sheeran at Wembley.
Several seaside destinations will have no services, including Bournemouth, Blackpool, Margate, Llandudno, and Skegness. And no trains will also be running in Cornwall.
Services across England, Wales and Scotland will primarily be restricted to main lines, and those will only be open between 07:30 and 18:30 BST.
Passengers with pre-booked tickets for Saturday are able to travel on Sunday or Monday instead, or claim a refund.
The Rail, Maritime and Transport (RMT) union is looking for a pay rise of at least 7% and assurances of no compulsory redundancies.
The union, whose members include everyone from guards and signallers to catering staff and cleaners, says an offer of a 2% pay rise, with the possibility of a further 1%, was “unacceptable”, pointing to the rising cost of living.
Network Rail said it would consider a pay rise above 3%, but only if the union agreed to modernise working practices.
RMT general secretary Mick Lynch said members are “standing up for all working people trying to get a pay rise and some job security”.
But, on the eve of the third walkout, Transport Secretary Grant Shapps urged the union not to “keep hamstringing the country”, adding they should “agree a deal to bring our rail industry into the 21st Century”.
Union bosses have warned more strikes are likely if a settlement cannot be reached.
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