DENPASAR, Indonesia (Reuters) - Bali Governor Made Mangku Pastika said the closure of I Gusti Ngurah Rai International Airport could last longer than 24 hours amid an eruption of Mount Agung.   We don t know how long it will be closed for,  Pastika told reporters, referring to the Bali airport.  Sure, it s been closed for 24 hours until tomorrow, but that doesn t rule out the possibility the (closure) could be extended,  he said.  At least 5,000 foreign and 15,000-20,000 domestic tourists pass through the airport each day, according to Pastika.  Ngurah Rai is Bali s main international gateway and a hub for tourists traveling to Indonesian islands further east.  