The convoy of 10 trucks carrying 90 tonnes of food and basic medical supplies travelled from the capital Beirut down a so-called humanitarian corridor, a route cleared with Israel beforehand to ensure the vehicles were not bombed.
"We hope this is the tip of the iceberg," said Khaled Mansour, UN spokesman in Lebanon, after the gruelling six-hour drive to Tyre. "We got here so it means the system is working, the humanitarian corridor is working."
The 90 tonnes of food will be distributed in Tyre by local groups and the medical supplies - antibiotics, treatment for diarrhoea, stitches for small wounds - will go to a medical centre near Tyre.
The food can feed about 22,000 people for a week while the medical supplies should provide for 50,000 people for about three months, Mr Mansour said.
Young men unloaded the trucks, lugging sacks of wheat flour on their backs and stashing them in the underground parking lot of a bank.
The south of Lebanon has been blasted by Israeli shells for the past 15 days and heavy fighting between the Israeli army and Hezbollah guerrillas has sent hundreds of thousands of people fleeing the hilly border region.
Mr Mansour said the United Nations planned to send another aid convoy to Tyre from Beirut tomorrow, two on Friday and more on Saturday, hopefully establishing the humanitarian corridor as a "regular process".
Concerns for civilians
He said aid workers were concerned about the welfare of civilians trapped in the border town of Rmeish, sandwiched between the Israeli border and the Lebanese town of Bint Jbeil, the scene of intense battles.
"This will be one of our major targets in the coming days," he said. The United Nations plans to inform the warring parties of plans to deliver aid to try to secure guarantees of safe passage.
"Lebanon has enough food, the roads are the issue," said
Mr Mansour, the boom of Israeli shells echoing from the hills just outside Tyre.
As the aid convoy headed south hundreds of cars streamed north on the road from Tyre, crammed with men, women, children and babies, desperate to escape the shelling and fierce fighting near Lebanon's southern border with Israel.
Two Jordanian military planes landed at Beirut's international airport to evacuate those seriously wounded.
Airport officials said the aircraft were the first to land at Beirut's airport since July 13 when Israeli warplanes bombed its runways and forced it to close.
Subsequent strikes on the facility damaged fuel tanks and other installations.