SINGAPORE - There is no timeframe for reopening the world's biggest observation wheel because a review must be conducted into a breakdown which left 173 people trapped, a cabinet minister was quoted as saying Sunday.

Police are investigating after the Singapore Flyer stopped turning on Tuesday night, leaving scores of tourists stuck for more than six hours.

The Flyer's operating licence has been suspended while police investigate and it remains unclear how long the suspension will last.

Steven Yeo, the Flyer's general manager, said earlier a small electrical fire had led to the stoppage, which he described as the fourth and most serious at the attraction since it opened in February.

"Given the nature of the incident and the fact that this is not the first time it has happened, obviously we need to be satisfied about what exactly happened first," Shanmugam was quoted as telling reporters.

Shanmugam, who is also Minister for Law, said the inquiry must also examine "what are the future probabilities" of a similar incident.

"We understand obviously the need for the Singapore Flyer to restart as quickly as possible. And it's got to be balanced against the public safety."

Most passengers were stuck inside the Flyer's enclosed cabins until power was restored but 10 escaped using rescue harnesses. Two were taken to hospital, officials said.

Police have said the Flyer would be allowed to resume operation once it has been certified as safe by an internationally-recognised body that assesses safety standards for amusement rides.

"Police investigations would cover how this problem occurred, how it can be prevented and what measures the operator can put in place to enhance passenger safety," they said in a statement Thursday.