A mistrial has been declared in the case of a Toronto mother accused of drowning her four-year-old autistic child.

The second-degree murder trial for 36-year-old Xuan Peng was unexpectedly halted on Tuesday, one week after it began, after a second juror could not fulfill their duty.

Last Thursday, the jury was pared from 12 members to 11 after a male juror suffered a non-fatal heart attack.

Another juror was lost on Monday night after being arrested for a "serious driving charge," a lawyer told CTV News. It's not clear what the specific offence is or in which jurisdiction it was laid.

Madam Justice Mary Lou Benotto on Tuesday said she felt she had no choice but to declare a mistrial as 10 jurors would not be sufficient to conduct what's expected to be an eight-week trial, CTV's Chris Eby reported.

While 10 jurors is the minimum number required to render a verdict on a case, Benotto didn't want to risk another unforeseen circumstance and felt it was better to pick another jury altogether, Eby said.

Jury selection for a new trial is scheduled to begin on Wednesday.

Peng, a Chinese immigrant, is accused of drowning her only daughter, Scarlett Chen, in the bathtub of their Scarborough home in July 2004.

She has pleaded not guilty.

With files from CTV's Chris Eby