Bernard Madoff, the New York broker accused of perpetrating an alleged $50bn fraud, was on Wednesday placed under curfew and required to submit to electronic monitoring by a US judge.

The judge's order, which modified Mr Madoff's original bail conditions, confined him to his Manhattan apartment from 7pm to 9am and was issued after prosecutors said Mr Madoff appeared unable to find enough co-signers for the $10m bond that was secured by his $7m Manhattan apartment.

Mr Madoff's wife was also ordered to surrender her passport and put up her properties in Montauk, New York and Palm Beach, Florida, to secure the bond, according to court documents. The number of co-signers was reduced from four - as originally required - to two.

Though Wednesday's bail hearing was canceled as a result, Mr Madoff appeared unexpectedly in a downtown Manhattan court in the afternoon.

Dressed in black and wearing a black baseball cap, Mr Madoff looked straight ahead and did not answer questions from reporters who rushed him as he left the building. "Why did you do it? Why did you confess?" reporters asked as he entered a black car.

He was mobbed by a huge crowd when he arrived later at his upper east side apartment building, and had to push through the crowd to get inside.

Mr Madoff, the founder of Bernard L. Madoff Investment Securities, already turned over his own passport after he was charged last Thursday with securities fraud after he admitted, according to court papers, that his advisory business was basically a giant "Ponzi" scheme and he had lost about $50bn.

Mr Madoff faces one count of securities fraud and separate civil charges by the US Securities and Exchange Commission.

His lawyer said that Mr Madoff's court appearance on Wednesday had to do with the bail conditions. Paperwork related to bail must be signed in person at the courthouse, people familiar with the matter said.

In the original bail agreement, the $10m bond was to be signed by four "financially responsible" people, including his wife. While his wife supported him, Mr Madoff had trouble rounding up others to pledge their financial support to him by the time of the original hearing set for Tuesday, according to people familiar with the matter.

Mr Madoff's two sons - who apparently alerted authorities to their father's confession of wrongdoing - are out of the question as co-signers, according to lawyers. Among Mr Madoff's friends, many of whom invested with him and appear to have lost money, support has also waned, people familiar with the situation said.

Court documents on Wednesday said that the defendant, his wife and his brother had signed the bond.