One official, speaking on condition of anonymity, told Reuters late on Monday the arms were found in two hideouts in the Libni mountain area in central Sinai.
The explosives were found during a police raid in the area of al-Maghara mountain, the official said. It was not clear if the weapons or the explosives were destined for smuggling into
the Palestinian territories, he added.
Israel has said repeatedly that tons of munitions and explosives are being smuggled through tunnels from Sinai into the Gaza Strip but has presented scarce evidence that Gaza gunmen use such weaponry.
Monday's find brings to more than four tons the explosives that Egyptian police have seized in Sinai during November alone.
More than 100 people were killed in bomb attacks in tourist resorts in Sinai between October 2004 and April 2006.
Egypt has blamed the attacks on an Islamist militant group called al-Tawhid wal Jihad (One God and Jihad) and says the group is made up of Sinai Bedouin with militant views.