They were same type of tunnels that Israel, which destroyed 140 of them in its air campaign, says were used to smuggle in rockets that lashed its cities and towns by the hundreds during the recent fighting.
Gaza militant groups and Israel on Wednesday agreed to a truce, but Israel will not lighten its blockade of the enclave, Israeli sources said, as some Hamas officials had hoped it might. The Rafah border crossing with Egypt also remained mostly closed to traffic.
The impoverished enclave's food supply remained stable despite eight days of withering Israeli air assaults aimed at Palestinian militants, but medical supplies were running short.
Workers say the attacks destroyed more than two-thirds of the cross-border tunnels that bring cement, fuel and food -- as well as weapons -- into the coastal strip blockaded by Egypt and Israel since the Hamas Islamist group began its rule there in 2007.
"Our job is to bring the children and families of Gaza rice, chocolate and a way of surviving," said Hussein Seida, 21.
"We were afraid for our lives to come out and work in the last few days, but now we rebuild. We'll do anything to help our people, we'll build a tunnel to China if we need to," he said, clutching a hammer in his dirt-covered hands.
None of the tunnel workers interviewed said they had handled military materiel, and all said they were eager to reopen them for the sake of Gaza's civilians, and their own livelihoods.
"I can count the number of tunnels working now on one hand," said long-time tunneler Ahmed al-Aida. "There's so much work to be done before we can get back to normal."
Wednesday's ceasefire ended eight days of lopsided fighting in Gaza and Israel that killed more than 160 Palestinians and six Israelis.
For the more than 1,000 wounded Palestinians recovering in hospitals, deliveries of medicine by the World Health Organization and other aid agencies after the ceasefire arrived just in time.
"But for many people, the aid that arrived was too little, too late," Willow Heske of global aid organization Oxfam said.
Basic medicines in Gaza have run low since Palestinian factions fought a brief civil war in 2007, cutting off Gaza from medical supplies in the West Bank.
As casualties poured into Gaza's overwhelmed hospitals during the bombings, the dearth of medicines grew worse, but stocks are now being returned to pre-crisis levels. The World Health Organization rushed 11 truckloads of medical supplies through a border crossing specially opened by Israel.Stores buzzing again
Food stocks stayed stable during the fighting in Gaza, where international food aid and imports are critical. The main commercial crossing, Kerem Shalom, was shut on Tuesday after it was hit by mortars, but has since resumed operations.
Cocoa Puffs cereal, potato chips and pasta of all kinds piled the shelves of supermarkets, but the aisles were devoid of customers who chose to stay home as Israeli drones and distant airstrikes shook the air before the ceasefire took effect.
Gaza farmers, fisherman and traders were especially hard-pressed by the violence, as many skipped work for the last week to dodge the bombs. But not everyone did so.
As Tamer Bashier, 31, an impoverished produce vendor ventured out by motor rickshaw to replenish his stocks on Tuesday, he was killed in an Israeli air strike, said the Ma'an Development center, a local aid organization linked to Oxfam.
Now safe to travel, Gaza's streets are packed.
The al-Qishawi supermarket in downtown Gaza city, derelict just hours before, teemed with families on Thursday morning as stock clerks wheeled carts of canned beans down the aisles.
"Do you see how things changed for us so totally," Hussein Qishawi beamed, waving groceries past the check-out scanner.
"Yesterday people were stuck in their houses, and when they came, they bought enough to last them for days. Now we're almost back to normal, thank God."
RAFAH (Reuters) -- Knee-deep in craters carved out by Israeli air strikes, Palestinians wielded shovels and sandbags to reopen tunnels used to smuggle in goods from Egypt to Gaza, while international aid agencies raced to replenish Gaza's depleted supplies.