The president of US TV network NBC has hinted at the possibility of hit sitcom Friends remaining on air beyond its forthcoming ninth - and reportedly final - series.

The show, which is one of the top-rated programmes in the US, is scheduled to broadcast its final episode next May.

However, NBC's Jeff Zucker has left open the possibility that the show could continue, saying that it would be impossible to replace.

"There's no question that when Friends leaves our schedule, we'll have a gaping hole," he said.

"I would say in all candour that it's probably the final season of Friends. And I'd be surprised if it weren't. But I wouldn't 100% put the nails in the coffin yet."

There's no question that when 'Friends' leaves our schedule, we'll have a gaping hole,

Jeff Zucker, President, NBC

The show's producers remain convinced that the next series will be the last, and are preparing their storylines accordingly.

"We have the feeling that creatively we're there," said Marta Kauffman, one of the co-creators of the show.

"It's not... that we couldn't come up with another season if that were in front of us... but we don't want to overstay our welcome."

Her producing partner, David Crane, said that they still had no idea how the final series might end.

"We haven't really figured that out yet," he admitted, adding that while the final episode may not tie up every loose end, the writers of the show were determined to end the series happily.

"I guarantee they won't end up in jail," joked co-producer Kevin Bright, referring to the finale of the hit NBC sitcom Seinfeld.

Aniston's Rachel gives birth in the current series

Each of the six principal cast members of the show currently earns a reported $1m (�600,000) per episode.

NBC and Warner Bros, who make the show, both said in February that the next series would be the last, with many suggesting it had reached its peak.

However, the most recent series, which ended with Rachel (Jennifer Aniston), giving birth to a child fathered by Ross (David Schwimmer) was one of the most popular yet and has garnered a clutch of Emmy nominations.