About 1,900 members of the Unite union at Felixstowe in Suffolk are walking out for eight days in a dispute over pay.
Unite said members rejected a 7% pay offer from the Felixstowe Dock and Railway Company, which it said was below the rate of inflation.
A port spokesman said the strike was "disappointing".
A picket line formed early on Sunday as the strike began, and the union said it would be manned until 22:00 on each day of the walkout.
Miles Hubbard, from Unite's regional office, told BBC: "Very few people reported for work this morning.
BDP is aware of the announced eight-day strike action at the Port of Felixstowe. Hutchison Ports and the Union Unite have been unable to reach an agreement after a revised pay offer was put to workers but rejected by the hourly branch of Unite. At this moment, no further talks are scheduled.
The strike action began on Sunday 21st August and is planned to end on Monday 29th August, it is subject to change as the situation evolves further.
It is expected to cause operational delays. Potential impact could be port diversions, container collections, and deliveries. Vessel ETAs into Felixstowe could be either significantly advanced or delayed in order for carriers to maximise available labour immediately before and straight after the strike period. These will affect both import and export shipments.
For import cargo currently at the terminal, we strongly encourage you to contact us to arrange delivery asap.
BDP will continue to monitor vessel arrivals and advise you if your shipment is affected. Please contact your local BDP representative if you have any questions or concerns.