LONDON — Eurotunnel says passengers are facing a second day of disruption on the cross-Channel service because of extreme temperatures under Britain’s heatwave.

The company has cancelled thousands of tickets for passengers returning on the same day, or on Saturday, in an effort to ease long lines.

Passengers faced delays of up to six-and-a-half hours on Thursday when train air conditioning units failed. On Friday, the operator warned of delays of three-and-a-half hours.

A statement from Eurotunnel says they are unable to check in anyone arriving more than two hours before their booked crossing time.

This is one the busiest weeks of the year for cross-Channel travel, as the start of many school summer holidays leads to a surge in family trips.