As the audience settled into their seats, musicians from orchestras across Europe, who have come together for the special performance, stepped onto the stage for a last minute practice under draped white fairy lights.
The "peace concert" marks the first time that Barenboim, an outspoken proponent of peace between Israel and the Palestinians, has visited Gaza.
He will be conducting musicians from five European orchestras through a programme of pieces by Mozart including Eine Kleine Nachtmusik and the G minor symphony.
As the musicians, dressed smartly in black suits, tuned their instruments, audience members said they were thrilled to be part of the rare event and heartened that an Israeli had chosen to come to Gaza.
The enthusiastic crowd leapt to their feet as Barenboim entered the hall.
In brief remarks, he said he had gathered a group of musicians with "two things in common: they are tremendously good musicians... and they are musicians who care about humanity."
"This is a unique gesture from the whole of Europe for you, Gaza," he added, to thunderous applause.
Fatma Shahin, a 28-year-old English teacher who was accompanying some of her students, said they were excited for the concert. "The girls will like it. It may change something in their minds and give them a chance to think before judging people," she said, adding that it was significant that an Israeli had chosen to come to Gaza to perform. "It will really make a difference, because he's bringing a message of peace."
Barenboim is well known for his calls for peace between Israel and the Palestinians, and in 1999 co-founded a "peace orchestra" with his friend Edward W. Said, a Palestinian-American scholar who died in 2003.
Known as the East-West Divan orchestra, it brings together Israeli, Arab and international musicians, and in 2005 it performed in the West Bank city of Ramallah.
The composer, who holds Israeli, Argentine and Spanish passports, in 2008 accepted honorary Palestinian citizenship saying he hoped the move would be an example of the "everlasting bond" between Israelis and Palestinians.
"I know that Barenboim is a messenger of peace in the Middle East and for the Palestinians and I believe music can make peace between people," said Natalie Nahel, a 24-year-old translator. "Culture, literature, music and education are all important for creating peace between countries."
Barenboim has performed across the West Bank, but never in the Gaza Strip. He has sought Israeli permission to cross into the coastal territory several times to perform, but was refused. Organisers said Barenboim, who was accompanied by his wife and two of his sons, crossed into Gaza for the concert from the Rafah crossing on Gaza's border with Egypt.