The blast drew criticism from Russia, Japan, the US, the European Union and South Pacific countries. The French opposition Socialists said the series should be halted.
The test was at Fangataufa atoll, 25 miles from Muroroa (where the first explosion took place on 5 September), shortly after 12.30am British time on Monday. Fangataufa is used for testing particularly powerful bombs, and the device was equivalent to 110,000 tons of TNT, compared with 20,000 tons in the earlier test.
The explosion should have created a cavern 100 yards across, against 60 yards for the Mururoa test. The rock above would then have collapsed into the cavern, causing slight subsidence on the surface. Fangataufa is smaller than Mururoa, but has been used for only nine tests, compared to 127 on the larger island. Patricia Lewis, of the Verification Technology Information Centre, which monitors nuclear tests, said that an explosion the size of Monday's might have started to break Mururoa apart.
Unlike the first test, which was designed to help scientists prepare a simulation programme that would make experiments with real weapons unnecessary, the Fangataufa explosion tested a new warhead, the TN-75, which is to be carried by submarines of the Triomphant class. The Triomphant should be commissioned next year, and will carry 16 missiles, each equipped with six TN-75 warheads. Test data is also expected to be used in designing a warhead for a new long-range cruise missile.
Opinion polls indicate a clear majority in France opposed to the tests, and the decision to resume them is held partly responsible for the slide in the popularity of President Jacques Chirac. The next test is expected in three to five weeks. Mr Chirac has hinted that the programme of eight tests may be reduced to seven or six.
Dr Lewis expected the remainder to be relatively small, although she did not rule out the possibility of testing a full-size cruise missile warhead.