Ratko Mladic's genocide trial was halted for the second day running because the former Bosnian Serb military commander was still undergoing medical tests after being rushed to hospital yesterday.

Mladic's seat in the Yugoslav war crimes tribunal courtroom in The Hague was empty as the trial briefly resumed and Presiding Judge Alphons Orie said Mladic was still undergoing a test that required him to be under observation for 24 hours.

Mladic's lawyer said he initially feared the 70-year-old former general had suffered a stroke when he complained of feeling ill in court but that tests had ruled that out.

"Now we think either it's a high level of sugar in his blood or high blood pressure, since he had both higher than normal yesterday," Branko Lukic told reporters outside the courtroom. "We are hopeful that we will continue on Monday."

However, Lukic warned that Mladic's frail health could be imperilled by his trial and hinted he would apply to further reduce the time he spends in court each week.

The complex trial, covering atrocities spanning the entire 1992-1995 Bosnian war that left 100,000 people dead, is expected to last years and has so far had sittings scheduled for only one morning or afternoon session per day.