LONDON — Sixty-eight migrants, including two pregnant women and 15 children, have been found locked inside four trucks at a port in southeast England, the authorities said on Friday.

The Home Office said that four Polish truck drivers had been arrested after the discovery, a reminder of the extreme measures that migrants will take to find refuge in Europe.

The East of England Ambulance Service said several of the migrants, who had been crammed into and locked inside trucks discovered Thursday night at Harwich International Port in Essex, were suffering from chest and abdominal pain and were feeling faint.

Seven people, including two women, were taken to the hospital, while the remainder were turned over to the border authorities. The Home Office said the migrants — 35 Afghans, 22 Chinese, 10 Vietnamese and one Russian — were discovered by Border Force officers after they searched several vehicles.