Loose drain cover halts Formula One day two testing in Bahrain

Both Hamilton and Leclerc hit the debris at Turn 11 in Bahrain, and the running was red-flagged with one hour and 40 minutes remaining.

Circuit officials attempted to repair the track, but after a delay of nearly 40 minutes, it was announced that the running would not resume.

The one-hour lunch break, was brought forward by an hour. The afternoon session will now run for five hours, instead of four, starting one hour earlier than planned at 2pm local time (11am GMT).

Ferrari said the impact caused damage to the floor of Leclerc's Ferrari, which has since been replaced.

It is unclear at this stage how extensive the damage was to Hamilton's Mercedes.

Both Hamilton and Leclerc were unharmed in the incidents.

Last November, a water valve cover broke free from the newly-laid tarmac of the Las Vegas street circuit and tore into the underbelly of Carlos Sainz's Ferrari at 210mph.

Speaking at the time, Ferrari team principal Fred Vasseur called the incident "unacceptable".

Hamilton, competing in his final season for Mercedes ahead of his switch to Ferrari, is scheduled to be behind the wheel of his new machine all day. He was sixth when the red flag was deployed.

Max Verstappen finished fastest on Wednesday. The test concludes on Friday ahead of next Saturday's first round of the season, also in the Gulf kingdom.

Read More: F1: Red Bull's Max Verstappen fastest in Bahrain testing session (planetsport.com)